Global SARS-CoV-2 seroprevalence from January 2020 to April 2022: A systematic review and meta-analysis of standardized population-based studies

Limitations of neutralizing antibody titers in COVID-19 vaccine efficacy trials and a call for additional correlates of protection

The coronavirus disease (COVID-19) pandemic accelerated development of various vaccine platforms. Among them, mRNA vaccines played a crucial role in controlling the pandemic due to their swift development and efficacy against virus variants. Despite the success of these vaccines, recent studies highlight challenges in evaluating vaccine efficacy, especially in individuals with prior COVID-19 infection. Weakened neutralizing antibody responses after additional doses are observed in these populations, raising concerns about using neutralizing antibody titers as the sole immune correlate of protection. While neutralizing antibodies remain the primary endpoint in immunogenicity trials, they may not fully capture the immune response in populations with widespread prior infection or vaccination. This review explores reduced neutralizing antibody responses in previously infected individuals, and their impact on vaccine efficacy evaluation. It also offers recommendations for improving efficacy assessment, stressing incorporation of additional immune markers such as cell-mediated immunity to enable more comprehensive understanding of vaccine-induced immunity.

Preventing respiratory viral transmission in healthcare settings

PURPOSE OF REVIEW

The COVID-19 pandemic catalyzed new insights into respiratory viral transmission mechanisms and prevention. We review the most practical and impactful measures to prevent SARS-CoV-2 and other nosocomial respiratory viral infections in healthcare.

RECENT FINDINGS

Nosocomial respiratory viral infection rates mirror viral activity levels in the surrounding community. During peak periods ∼15-20% of hospitalized patients with respiratory viral infections may have acquired their virus in the hospital. Nosocomial respiratory viral infections are associated with increased lengths-of-stay, risk of respiratory failure, and hospital death. Most procedures contribute minimally to aerosol production compared to labored breathing, coughing, and forced expiration. Masking for source control and exposure control both decrease transmission risk, respirators more so than masks. Likewise, vaccinating healthcare workers decreases transmission risk and is associated with lower patient mortality rates, particularly in long-term care facilities. Increasing air changes, ultraviolet irradiation, and portable HEPA filtration units may also decrease transmission rates but their marginal benefit relative to current healthcare ventilation standards has yet to be established.

SUMMARY

Practical strategies to prevent nosocomial respiratory viral infections include maximizing staff and patient influenza and SARS-CoV-2 vaccination rates and implementing routine masking during patient interactions when community incidence is high.

Paradoxical increase in global COVID-19 deaths with vaccination coverage: World Health Organization estimates (2020-2023)

BackgroundMany reports on the impact of vaccination on COVID-19 pandemic deaths were projections undertaken as the global emergency was unfolding. An increasing number of independent investigators have drawn attention to the subjective nature and inherent biases in mathematical models used for such forecasts that could undermine their accuracy when excess mortality was the metric of choice.ObjectiveCOVID-19 deaths were compared between the pre-vaccines and vaccination eras to observe how vaccination impacted COVID-19 death trajectory worldwide during the pandemic emergency.MethodsCOVID-19 cases, deaths and vaccination rates in World Health Organization (WHO) database till 07 June 2023, Case fatality rate per 1000 for the pre-vaccines period (CFR1), and that over vaccination era (CFR2) were compared for all WHO regions, while tests of correlation between the percentage change in COVID-19 deaths and variables of interest were examined.ResultsCOVID-19 deaths increased with vaccination coverage ranging from 43.3% (Africa) to 1275.0% (Western Pacific). The Western Pacific (1.5%) and Africa (3.8%) regions contributed least to the global cumulative COVID-19 deaths pre-vaccines, while the Americas (49.9%) and Europe (27.6%) had the highest counts. The Americas (39.8%) and Europe (34.1%) accounted for >70% of global COVID-19 deaths despite high vaccination, and the percentage increase in COVID-19 mortality and the percentage of person's ≥65 years were significantly correlated (0.48) in Africa.ConclusionCOVID-19 mortality increased in the vaccination era, especially in regions with higher vaccination coverage.

Long-lasting antibody B-cell responses to SARS-CoV-2 three years after the onset of the pandemic

Immune memory is essential for the effectiveness of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccination. In the current context of the pandemic, with a diminished vaccine efficacy against emerging variants, it remains crucial to perform long-term studies to evaluate the durability and quality of immune responses. Here, we examined the antibody and memory B-cell responses in a cohort of 113 healthcare workers with distinct exposure histories over a 3-year period. Previously infected and naive participants developed comparable humoral responses by 17 months after receiving a full three-dose mRNA vaccination. In addition, both maintained a substantial SARS-CoV-2-reactive memory B-cell pool, associated with a lower incidence of breakthrough infections in naive participants. Of note, previously infected participants developed an expanded SARS-CoV-2-reactive CD27-CD21- atypical B-cell population that remained stable throughout the follow-up period. Thus, previous SARS-CoV-2 infection differentially imprints the memory B-cell compartment without compromising the development of long-lasting humoral responses.

Post-Omicron SARS-CoV-2 antibody prevalence in Sierra Leone: A cross-sectional, nationally representative, follow-up serosurvey

Based on a serosurvey conducted in March 2021, Barrie and colleagues published the first nationally representative SARS-CoV-2 serosurvey in Africa, estimating a SARS-CoV-2 seroprevalence of 2.6% in Sierra Leone, 43 times higher than the reported number of cases at that time. Over the following two years, increasingly transmissible variants-specifically Delta and Omicron-proliferated across the globe, and their impact in Africa is poorly understood. Additional nationally representative seroprevalence data are therefore necessary to understand the pandemic's progression on the continent and for evaluating containment measures and future preparedness. Our follow-up nationally representative survey was conducted in Sierra Leone from February to March 2023. We returned to the 120 Enumeration Areas throughout the country collecting blood samples from one or more individuals per household as well as information on sociodemographic characteristics, history of COVID-19 infection and immunization, and attitudes towards vaccination. The weighted overall seroprevalence (vaccinated and/or SARS-CoV-2 infection) for individuals >19 years of age was 33% (95% CI 29-37). Using the data and distributions from our previous serosurvey, the weighted predicted seroprevalence (any prior SARS-CoV-2 infection) for the general population was 28% (95% CI 15-41). The weighted predicted seroprevalence was ~11 times higher than the pre-Delta/Omicron prevalence. It was also over 300 times higher than the reported number of cases. Despite this, overall seroprevalence was low compared with countries in Europe and the Americas (pointing towards lower transmission in Sierra Leone). In addition, our results suggest the following regarding prevention campaigns claiming to have vaccinated 70% of adults in Sierra Leone as of December 2022: 1) they resulted in limited seroconversion; 2) there was significant waning of immunity; and/or 3) many less individuals were vaccinated than reported. Regardless of the cause, the utility of COVID-19 Vaccine Delivery Partnership (CoVDP) efforts three years into the pandemic is called into question.

The COVID-19 pandemic in children and young people during 2022-24: what new did we learn?

The research conducted between 2022 and 2024 has advanced our understanding of COVID-19 in children and young people (CYP), particularly with the emergence of the Omicron variant and its subvariants. The findings have reinforced that, while Omicron infections are often milder compared to earlier variants, the overall seroprevalence of SARS-CoV-2 in children has increased, with notable regional and demographic disparities. COVID-19-related hospitalisation rates in children rose during Omicron waves, especially among infants, unvaccinated individuals, and CYP at higher risk, i.e. with comorbidities such as obesity, diabetes, and neurological or cardiac conditions. Despite this, severe disease and mortality in children remained very low. The observed increases in type 1 diabetes incidence and multisystem inflammatory syndrome in children (MIS-C) have also highlighted the broader systemic effects of SARS-CoV-2 in paediatric populations. Evidence has underscored the protective effect of vaccination in preventing severe disease and MIS-C and vaccine safety, emphasising the need for targeted immunisation strategies, particularly among children who may be at higher risk. Studies have also estimated that a significant proportion of children experienced persistent post-COVID-19 infection symptoms such as fatigue, mood disturbances, sleep disorders, and respiratory difficulties, but the reported prevalence varied widely, from as low as 1.6% to as high as 70%, due to differences in study methodologies, case definitions, and populations studied. Standardised definitions and measurement tools, such as those developed through international consensus processes, are required to improve diagnosis, treatment, and research into this persisting condition. Ethnic disparities in vaccine uptake persist, implying that vaccine hesitancy and accessibility, alongside approaches to countering disinformation, are important areas for future research.

Comparative spatial-temporal analysis of SARS-CoV-2 lineages B.1.1.33 and BQ.1.1 Omicron variant across pandemic phases

The evolution of COVID-19 pandemic has been characterized by the rapid emergence of new SARS-CoV-2 variants, each of which poses unique challenges to public health. This study analyzes the dispersion profiles during the Pre-Omicron and Post-Omicron phases in different epidemiological contexts. The Brazilian state of Espirito Santo, despite its low population density, plays a critical role as a commercial hub due to its intense port activity, which may have contributed to COVID-19 cases and mortality rates being higher than the national average. The state recorded 34,000 confirmed cases and 377 deaths per 100,000 inhabitants. Genomic surveillance revealed that the Pre-Omicron phase was dominated by the B.1.1.33 lineage, characterized by localized intraregional circulation. In contrast, the Post-Omicron phase, dominated by the BQ.1.1 lineage, exhibited greater diversity in circulating lineages, increased international interactions, and rapid viral dissemination, highlighting distinct transmission dynamics between such periods. This study highlights the need for adaptive public health strategies that account for both viral behavior and regional socioeconomic factors, while highlighting the strategic importance of Espirito Santo in monitoring SARS-CoV-2 evolution.

The effect of COVID vaccination timing on the seroprevalence of IgG antibodies: evidence from the Guayas region of Ecuador

Background and aims

Timely distribution of COVID-19 vaccines was particularly important for developing countries that do not have strong health systems and related infrastructure. We analyze data from the Guayas province of Ecuador, an area particularly affected by the pandemic, to determine the seroprevalence of SARS-CoV-2 and the effect of the timing of the second dose of COVID-19 vaccines on the seroprevalence SARS-CoV-2 IgG antibodies.

Methods

This cross-sectional study involved 1,761 individuals aged 18 and older who voluntarily enrolled prior to and during the initial phase of vaccine rollout in Ecuador (October 2020 to July 2022). IgG anti-SARS-CoV-2 RBD antibodies were assessed by an in-house ELISA to evaluate the immune response to Pfizer (BioNTech, Spike mRNA) and AstraZeneca (Oxford, AstraZeneca Spike) vaccine in the Guayas province. Ordinary least squares (OLS) regressions were employed to determine the effect of delayed second doses later than prescribed by the manufacturer for both vaccines.

Results

Before the vaccination campaign, we estimated an RBD IgG seroprevalence of 27.7% (95% CI: 23.6-27, n = 469). The estimate increased to 89.4% (95% CI: 87.7-91.18, n = 1,235) after the first vaccine dose and to 92.6% (95% CI: 90.7-94.5, n = 748) after the second dose. Individuals who received the second dose of the Pfizer vaccine later than the recommended dose showed significantly lower levels of IgG antibodies 2-3 weeks after receiving the second dose than those who received the dose within the recommended timeframe. Furthermore, we did not find any effect on RBD IgG antibody levels in those who received a second dose of the AstraZeneca vaccine during the first and second parts of the recommended vaccination window.

Conclusion

The results suggest that a significant portion of the study population was already infected with SARS-CoV-2 prior to the vaccination. As expected, seropositivity increased alongside vaccination efforts. We determined that Pfizer vaccine recipients should be adhered to vaccine timing guidelines. Furthermore, resource-limited countries should consider administering vaccines with flexibility in dosing intervals, such as AstraZeneca, as it allows for a wider time frame without significantly reducing the boosting of IgG antibodies.

Determinants and dynamics of the seroprevalence of anti-SARS-CoV-2 antibodies in Poland

PURPOSE

In the present study, we aimed to assess the anti-SARS-CoV-2 antibodies in population and in convalescents 6 months after infection with COVID-19.

PATIENTS AND METHODS

The study population consisted of 2 groups, i.e. group I: 232 post-COVID-19 patients, and group II: 544 patients from a population cohort. Detection of anti-N antibodies was performed with Elecsys Anti-SARS-CoV-2 and anti-S antibodies with LIAISON SARS-CoV-2 S1/S2 IgG tests.

RESULTS

After the Omicron wave, gradual increase in the prevalence of the analyzed antibodies was observed in the general population - up to 92.5 ​% of anti-S and 69.7 ​% of anti-N antibodies. In the COVID-19 convalescents, 6 months after infection, 4.3 ​% and 3.7 ​% did not generate significant titers of anti-S and anti-N antibodies, respectively. Among patients, who were vaccinated, 1 ​% did not generate anti-S antibodies. The median age of non-responders was higher than that of responders. Sex did not influence the results. Comparison of anti-N and anti-S antibodies 6 months after infection in the whole group showed higher anti-N titer in patients who suffered from the disease than in the general population. In the general population, 17.4 ​% of participants had anti-N antibodies, and 9 ​% had anti-S antibodies, despite no prior vaccination or history of COVID-19.

CONCLUSIONS

High prevalence of anti-N antibodies in patients reporting no history of COVID-19 during last wave, even after official end of the pandemic suggests high prevalence of SARS-CoV-2 in the environment and frequent asymptomatic or unspecific COVID-19, what is of high importance from the public health perspective.

Implementing SARS-CoV-2 routine surveillance in antenatal care in Zambia, 2021-2022: best practices and lessons learned

BACKGROUND

In Zambia, the true extent of SARS-CoV-2 infections is unknown because initial surveillance focused on patients with symptoms or severe disease. Antenatal sentinel surveillance had not been used to assess infection trends. The ANC COVID-19 surveillance study sought to determine SARS-CoV-2 seroprevalence and COVID-19 vaccine uptake among pregnant women. We provide insight into the study implementation, challenges encountered, best practices, and lessons learned.

METHODS

A repeated cross-sectional seroprevalence survey was implemented at 39 health facilities in four districts from September 2021 to September 2022. Pregnant women aged 15-49 years were enrolled at their first antenatal care visits. An electronic questionnaire gathered demographics and other COVID-19 related information from consenting participants. A dried blood sample was collected to detect IgG antibodies using a multiplex bead assay. Seropositive results were categorized as infection, infection and vaccination or infection based on anti-RBD and anti-nucleocapsid test results. Problems and their root causes were identified as they occurred. Practical problem-solving strategies were devised, implemented, and monitored to ensure that goals were accomplished.

RESULTS

In the primary analysis, 7% of the 9,221 samples collected from participants were not tested because they were missing. COVID-19 vaccine uptake of 9,111 pregnant women was assessed. Approximately 64% of participants were cumulatively seropositive for SARS-CoV-2 antibodies. Seroprevalence increased from 27.8% in September 2021 to 56.6% in July 2022. We observed an increase in vaccine coverage (0.5-27%) over time. Women aged 40-49 years old, without education and with prior COVID-19 infection were associated with higher vaccine uptake. The Delta variant of COVID-19 and the reallocation of health facilities between two partners delayed surveillance activities and increased the cost of implementation (e.g., the purchase of additional calibration and validation kits and DBS cards). Protocol deviations were attributed to the lack of experience in conducting research but, the district RAs repeatedly trained health facility staff to enhance their research knowledge.

CONCLUSIONS

Incorporating SARS-CoV-2 surveillance into routine antenatal care is feasible and potentially sustainable when existing health system infrastructure, human resources, and surveillance systems are leveraged. Yet, careful planning is needed to anticipate implementation challenges and ensure high-quality data collection.

Population shift in antibody immunity following the emergence of a SARS-CoV-2 variant of concern

Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) variants of concern (VOCs) exhibit escape from pre-existing immunity and elicit variant-specific immune responses. In South Africa, the second wave of SARS-CoV-2 infections was driven by the Beta VOC, which coincided with the country-wide National COVID-19 Antibody Survey (NCAS). The NCAS was conducted between November 2020 and February 2021 to understand the burden of SARS-CoV-2 infection through seroprevalence. We evaluated 649 NCAS sera for spike binding and pseudovirus neutralizing antibodies. We classified individuals as ancestral or D614G neutralizers (114/649), Beta neutralizers (96/649), double neutralizers (375/649) or non-neutralizers (62/649). We observed a consistent decrease in preferential neutralization against the D614G variant from 68 to 18% of individuals over the four sampling months. Concurrently, samples with equivalent neutralization of both variants, or with enhanced neutralization of the Beta variant, increased from 32 to 82% of samples. Neutralization data showed that geometric mean titers (GMTs) against D614G dropped 2.4-fold, while GMTs against Beta increased 2-fold during this same period. A shift in population humoral immunity in favor of Beta-directed or cross-neutralizing antibody responses, paralleled the increase in genomic frequency of the Beta variant in South Africa. Understanding similar population immunity shifts could elucidate immunity gaps that drive SARS-CoV-2 evolution.

Genomic Epidemiology of the Main SARS-CoV-2 Variants Circulating in Italy During the Omicron Era

Since early 2022 the Omicron variant has rapidly spread worldwide, becoming the dominant variant to date. The study aimed to investigate the clinical and epidemiological characteristics of COVID-19 patients and reconstruct the genomic epidemiology of main SARS-CoV-2 Omicron sublineages in Italy in 2022. A total of 8970 SARS-CoV-2 samples were studied, and phylogenetic analyses were focused on BA.1, BA.2, and BA.5 subvariants. More than half of subjects received three doses of vaccine and experienced a reinfection. A significant larger proportion of unvaccinated subjects presented reinfection compared with vaccinated. Clusters presented a tMRCA between September-November 2021 (BA.1), November 2021-January 2022 (BA.2), and October 2021-May 2022 (BA.5). Re values showed the highest level between September-October, January-February 2022, and May 2022 for BA.1, BA.2 and BA.5, respectively. Limited number of studied variant sequences are included in clusters. The spread rate of the studied variant exceeded its evolutionary rate. No single sublineage had sufficient time to differentiate into large clusters, but only into small and fragmented groups sharing the same recent ancestor. These analyses dissect the epidemiological dynamics of Omicron sublineages in Italy over a period of great epidemiological changes in the COVID-19 epidemic.

Safety and immunogenicity of a single-dose omicron-containing COVID-19 vaccination in adolescents: an open-label, single-arm, phase 2/3 trial

BACKGROUND

Most individuals show immunity to SARS-CoV-2 from vaccination or infection, or both. We aimed to determine the safety and immunogenicity of an omicron-containing COVID-19 vaccine (mRNA-1273.222) in vaccine-naive adolescents who were SARS-CoV-2 positive.

METHODS

Part 3 of the phase 2/3 TeenCOVE trial was a phase 3, open-label, single-arm part done in the USA and the Dominican Republic that enrolled healthy, vaccine-naive adolescents (aged 12-17 years) to receive two 50 μg doses of mRNA-1273.222 (ancestral strain Wuhan-Hu-1 and omicron subvariants BA.4 and BA.5), 6 months apart. Primary reactogenicity and safety outcomes included assessment of solicited local or systemic adverse reactions 7 days after vaccination, and unsolicited and prespecified adverse events throughout study participation. Inferred effectiveness (primary immunogenicity outcome) was established by comparing neutralising antibody responses 28 days after dose 1 of mRNA-1273.222 in SARS-CoV-2-positive adolescents with responses 28 days after dose 2 of mRNA-1273 100 μg primary series in SARS-CoV-2-negative young adults (aged 18-25 years) from the COVE trial. This study is registered with ClinicalTrials.gov (NCT04649151).

FINDINGS

Between Dec 21, 2022, and June 5, 2023, 379 adolescents (378 of whom were SARS-CoV-2 positive) received at least one mRNA-1273.222 dose and were included in the safety analysis set. The reactogenicity profile was favourable compared with the mRNA-1273 primary series, with no new safety concerns identified. Unsolicited adverse events were reported in 49 (13%) of 379 participants; no deaths or adverse events leading to study discontinuation were reported. The immunogenicity set included 245 adolescents from the per-protocol immunogenicity subset who were SARS-CoV-2 positive at baseline and 296 young adults who were SARS-CoV-2 negative. Compared with the mRNA-1273 primary series in SARS-CoV-2-negative young adults, a single dose of mRNA-1273.222 induced superior (geometric mean ratio [GMR] 95% CI lower bound >1) neutralising antibody responses against omicron BA.4 and BA.5 (GMR 48·95 [95% CI 44·21-54·21]) and non-inferior (GMR 95% CI lower bound >0·667) neutralising antibody responses against ancestral SARS-CoV-2 (GMR 4·25 [95% CI 3·69-4·88]) in SARS-CoV-2-positive adolescents.

INTERPRETATION

In vaccine-naive, SARS-CoV-2-positive adolescents, single-dose mRNA-1273.222 was effective against COVID-19 based on successful immunobridging to the two-dose mRNA-1273 primary series in young adults. The findings support a simplified single-dose vaccination schedule with variant-containing mRNA vaccines, regardless of previous vaccination status.

FUNDING

Moderna.

Maternal and Placental Antibody Responses in SARS-CoV-2 Vaccination and Natural Infection During Pregnancy

BACKGROUND

As COVID-19 becomes endemic, understanding antibody response and transfer during pregnancy is crucial to inform policy and vaccination schedules. While good immunogenicity has been shown from SARS-CoV-2 vaccines, few data are available demonstrating functional responses in pregnant populations and infants.

METHODS

A prospective, multi-site observational study was completed across 14 centers in England from April 23, 2020, to December 21, 2022. Demographic, COVID infection and vaccination data were collected. Maternal and cord blood samples were taken at delivery, with maternal and neonatal blood samples taken at 6 weeks for participants who had been infected or vaccinated. Antibody concentrations were measured using antibody-dependent complement deposition, antibody-dependent neutrophil phagocytosis, ACE2 inhibition and Roche and EuroImmun antibody binding assays at the UK Health Security Agency.

RESULTS

Maternal vaccination and infection both produced an antibody response in 100% of mothers and 93.8% and 92.9% of neonates, respectively, which persisted at 6 weeks in 95%. The strongest response was seen in mothers who were both vaccinated and infected. Anti-spike antibody response decreased almost 25-fold from first to third trimester vaccination (P=0.013). Placental transfer of antibodies post-infection showed varied results depending on the assay used, with higher transfer ratios observed in assays measuring Fc-mediated antibody effector functions and IgG-specific responses.

CONCLUSIONS

Maternal vaccination is associated with good immunogenicity and successful antibody transfer to the neonate, particularly with vaccination in early pregnancy. Further study is needed to determine the mechanism by which the timing of vaccination affects antibody transfer. When measuring placental transfer of antibodies, consideration of the assay to use is essential.

High prevalence of undocumented SARS-CoV-2 infections revealed by analysis of nucleocapsid-specific IgG responses in diagnosed and undiagnosed individuals

Acute SARS-CoV-2 infections are not always diagnosed; hence an unknown proportion of all infections are not documented. SARS-CoV-2 can induce spike and nucleocapsid protein specific IgG antibodies, which can be detected in seroprevalence studies to identify a previous infection. However, with the introduction of vaccines containing the spike protein it is no longer possible to use spike-IgG as a marker of infection. In many countries marketed vaccines do not include the nucleocapsid protein, allowing the use of nucleocapsid-specific IgG (N-IgG) as a specific marker for previous infection. Importantly however, not all SARS-CoV-2-infected individuals develop detectable N-IgG responses and there are reports of waning of N-IgG titers in previously infected individuals, complicating the use of N-IgG in seroprevalence studies. Here, our aim was to investigate N-IgG as a marker for previous infection. To this end we analyzed a well characterized cohort (n = 2,583; sampled in March, 2022), including 612 participants with a previously diagnosed and documented SARS-CoV-2-infection. We show that 75% (460/612) of the confirmed SARS-CoV-2-infected participants were N-IgG positive, and that the frequency of seropositivity was stable for at least 105 weeks after the latest documented SARS-CoV-2-infection. Among participants with no documented SARS-CoV-2-infection, 32.6% (642/1971) were N-IgG-positive, suggesting a previous infection. Assuming similar frequency of N-IgG-seronegative cases in previously diagnosed and undiagnosed individuals we further estimate that 214 of the 1329 undiagnosed and N-IgG-negative cases had been previously infected, indicating a total infection rate of 56.8% (1,468/2,583), clearly higher than the documented 23.7% rate of infection, in this cohort. In conclusion, our results suggest that while N-IgG is a good marker of previous SARS-CoV-2-infection the large proportion of previously infected N-IgG-negative individuals introduces a risk for underestimations of total level of previously infected individuals in a population. Accounting for this dark number of undiagnosable cases can provide better estimates of total level of infected individuals in a population.

Strengthening serological studies: the need for greater geographical diversity, biobanking, and data-accessibility

Serological studies uniquely strengthen infectious disease surveillance, expanding prevalence estimates to encompass asymptomatic infections, and revealing the otherwise inapparent landscape of immunity, including who is and is not susceptible to infection. They are thus a powerful complement to often incomplete epidemiological and public health measures (administrative measures of vaccination coverage, incidence estimates, etc.). The recent surge in the deployment of serological surveys globally (in part due to the SARS-CoV-2 pandemic), alongside the development of new assays and new inference methods, means that the time is ripe to interrogate areas to strengthen future serosurveillance efforts. We identify three themes warranting attention: first, expanding the geographical diversity of these studies; second, investing globally in infrastructure for storage of blood samples (biobanking), opening the way to future analyses; and third, establishing protocols to increase data accessibility and to facilitate data usage for current and future studies. We conclude that strengthening serological studies is necessary and achievable through thoughtful sampling design, wide-scale sample storage, and thorough reporting practices.

Seroconversion and dynamics of IgG anti-SARS-CoV-2 antibodies during the pandemic: A two-month observation cohort study on the population of Sleman in Indonesia

BACKGROUND

This study describes the seroconversion and serodynamics of IgG antibodies against the RBD of SARS-CoV-2 in the general population of Sleman District, Yogyakarta Special Province. We aim to identify possible factors that correlate with the seroconversion and serodynamics of IgG antibodies against the RBD of SARS-CoV-2.

METHODS

We performed a longitudinal study of the population at Health and Demographic Surveillance System (HDSS) Sleman, Yogyakarta, Indonesia. Study subjects were recruited between April and December 2021 using convenience sampling and were followed up 2 times, i.e. 4-5 and 8-9 weeks. The inclusion criteria for subjects were age ≥ 18 years, absence of flu-like symptoms, and negative COVID-19 by using GeNose C19® screening. A community-based survey on demographics, comorbidities and smoking habits were documented at baseline, while a history of vaccination, COVID-19-related symptoms, mobility, and preventive measures, weight and height as well as a venous blood draw, were collected at each visit. The anti-RBD-SARS-CoV-2 IgG antibody concentration from blood plasma was measured using chemiluminescent microplate immunoassay (CMIA). Descriptive analysis was performed based on IgG seropositivity by using chi-squared test or Fisher's exact test, as appropriate. Logistic regression was subsequently performed to identify factors that were correlated with IgG seropositivity. Further, a grouping of subjects based on IgG seropositivity was done to analyze factors that might correlate with seroconversion and serodynamics of anti-RBD-SARS-CoV-2 IgG antibody. A P value ≤ 0.05 was considered to indicate a significant difference.

RESULTS

Three hundred eighty-five (385) participants were analyzed. At baseline, 307 out of 385 (79.7%) subjects were seropositive for the IgG antibody against the RBD of SARS-CoV-2. Descriptive analysis showed that sex, marital status, smoking habits, obesity, vaccination status, and preventive measures were different between the IgG anti-RBD-SARS-CoV-2 seropositive and negative individuals (p≤ 0.05). Further analysis showed that, vaccination was the factor most strongly correlated with seropositivity [OR = 20.58; 95% CI 10.82, 39.15]. Based on the correlation, we separated subjects into 4 groups. Group 1 (seronegative-unvaccinated individuals; 50 subjects); Group 2 (seronegative-vaccinated individuals; 27 subjects); Group 3 (seropositive-unvaccinated individuals; 25 subjects); and Group 4 (seropositive-vaccinated individuals; 282 subjects). During monitoring, 27/49 (55.10%), 5/25 (20%), 9/22 (40.91%), and 27/257 (10.51%) of subjects in Group 1, 2, 3, and 4 respectively, received 1 or 2 doses of COVID19 vaccine. When comparing seroconversion at baseline and monitoring 2, positive IgG seroconversion was observed in Group 1 (from 0/51 (0%) to 23/49 (46.94%)) and Group 2 (from 0/27 (0%) to 10/25 (40%)), but negative seroconversion was observed in Group 4 (from 282/0 (100%) to 248/257 (96.50%)); while, all subjects in Group 3 remained seropositive at the end of monitoring. This evidence suggested for hybrid immunity, on which infection and vaccine simultaneously contributes to anti-RBD-SARS-CoV-2 IgG seroconversion.

CONCLUSIONS

A high seroprevalence of the IgG antibody against RBD-SARS-CoV-2 in the Sleman population was found to correlate with COVID-19 vaccination and as infection occurred, thus enhancing hybrid immunity. We also identified nonresponder and rapid antibody decaying individuals, that call for targeted vaccinations in addition to annual universal boosting.

Modeling COVID-19 dynamics in the Basque Country: characterizing population immunity profile from 2020 to 2022

BACKGROUND

COVID-19, caused by SARS-CoV-2, has spread globally, presenting a significant public health challenge. Vaccination has played a critical role in reducing severe disease and deaths. However, the waning of immunity after vaccination and the emergence of immune-escape variants require the continuation of vaccination efforts, including booster doses, to maintain population immunity. This study models the dynamics of COVID-19 in the Basque Country, Spain, aiming to characterize the population's immunity profile and assess its impact on the severity of outbreaks from 2020 to 2022.

METHODS

A SIR/DS model was developed to analyze the interplay of virus-specific and vaccine-induced immunity. The model includes three levels of immunity, with boosting effects from reinfection and/or vaccination. It was validated using empirical daily case data from the Basque Country. The model tracks shifts in immunity status and their effects on disease dynamics over time.

RESULTS

The COVID-19 epidemic in the Basque Country progressed through three distinct phases, each shaped by dynamic interactions between virus transmission, public health interventions, and vaccination efforts. The initial phase was marked by a rapid surge in cases, followed by a decline due to strict public health measures, with a seroprevalence of 1.3 % . In the intermediate phase, multiple smaller outbreaks emerged as restrictions were relaxed and new variants, such as Alpha and Delta, appeared. During this period, reinfection rates reached 20 % , and seroprevalence increased to 32 % . The final phase, dominated by the Omicron variant, saw a significant rise in cases driven by waning immunity and the variant's high transmissibility. Notably, 34 % of infections during this phase occurred in the naive population, with seroprevalence peaking at 43 % . Across all phases, the infection of naive and unvaccinated individuals contributed significantly to the severity of outbreaks, emphasizing the critical role of vaccination in mitigating disease impact.

CONCLUSION

The findings underscore the importance of continuous monitoring and adaptive public health strategies to mitigate the evolving epidemiological and immunological landscape of COVID-19. Dynamic interactions between immunity levels, reinfections, and vaccinations are critical in shaping outbreak severity and guiding evidence-based interventions.

Longitudinal Follow-Up of the Specific Antibody Response to SARS-CoV-2 Vaccination in Colombia

A total of 5011 adult volunteers attending vaccination centers in different regions of Colombia were enrolled in a 1-year prospective observational cohort study to evaluate the immunogenicity and effectiveness of SARS-CoV-2-based vaccines as part of a National Vaccine Program established to contain the COVID-19 pandemic. Following informed consent, 5,011 participants underwent a sociodemographic survey and PCR testing to assess SARS-CoV-2 infection. Blood samples were collected, and serum fractions were obtained from a participant subsample (n = 3441) at six-time points to assess virus-specific IgG responses to the Spike protein, its Receptor Binding Domain, and the Nucleoprotein by ELISA. Additionally, antibody-neutralizing activity was evaluated using a cPass SARS-CoV-2 neutralization kit. Most participants (95.8%; n = 4802) received between one Ad26. COV2.S (Janssen vaccine) and four vaccine doses of BNT162b2 (Pfizer/BioNTech), AZD1222 (AstraZeneca), mRNA-1273 (Moderna), CoronaVac (Sinovac), with some receiving vaccine combinations; a small group, 4.2% (n = 209), remained unvaccinated. Throughout the study, only 8.76% (n = 439) of the participants tested positive for SARS-CoV-2 by PCR. Notably, all participants seroconverted for IgG antibodies, with high seropositivity rates for S (99.8%; n = 4795), RBD (99.7%; n = 1691), and N (92.7%; n = 3072) proteins. Moreover, significant (92%-97%) neutralizing activity was observed for all four SARS-CoV-2 circulating variants. This study highlights the importance of assessing the duration of the IgG response to SARS-CoV-2 elicited by vaccination and infection, and the antibody neutralizing activity as a potential surrogate marker of protection. These findings provide important insight for further strengthening the vaccination strategies to control COVID-19.

Establishing the African region monitoring vaccine effectiveness (AFRO-MoVE) network for respiratory pathogens

Population-level vaccination with newly developed vaccines to respond to the COVID-19 pandemic created a need to monitor vaccine effectiveness (VE) in the context of emerging SARS-CoV-2 variants and changing epidemiology. WHO and partners launched the African Region Monitoring Vaccine Effectiveness (AFRO-MoVE) Network in March 2021 to assess the performance of COVID-19 vaccines in real-world conditions in Africa. The Network aimed to facilitate and support comparable COVID-19 vaccine effectiveness studies in the African region, to provide a platform of scientific expertise and infrastructure, encourage the use of robust similar study designs to enable pooling to produce regional VE estimates and to build a sustainable network of hospitals, institutions, and experts to evaluate vaccines against pandemic and endemic respiratory pathogens. In the two years since its inception, the network has coordinated VE studies in the region and provided technical guidance and generic protocols employing robust methodologies. It brought together over 200 experts, representing 22 African countries and 55 organisations, and strengthened capacities by hosting ten webinars and six technical workshops. Of the 55 partners organisations, 25 based in 13 countries collaborated on implementing VE studies in the region. AFRO-MoVE supported study implementation in two phases, first targeting COVID-19 vaccination priority groups, then the general population. The network provides technical and financial support to nine studies, including three cohort studies in health workers and adults with comorbidities, and six test-negative design studies evaluating VE against symptomatic and severe disease. A data platform was established for pooled regional estimates. The AFRO-MoVE Network can form a sustainable platform to provide data for evidence informed decisions and timely VE monitoring for existing and new vaccines against respiratory pathogens and other diseases in the African region. Further development and consolidation of the network's activities can enable rapid response to future epidemics and pandemics.

Mucosal Immunization with an Influenza Vector Carrying SARS-CoV-2 N Protein Protects Naïve Mice and Prevents Disease Enhancement in Seropositive Th2-Prone Mice

Background/Objectives: Intranasal vaccination enhances protection against respiratory viruses by providing stimuli to the immune system at the primary site of infection, promoting a balanced and effective response. Influenza vectors with truncated NS1 are a promising vaccine approach that ensures a pronounced local CD8+ T-cellular immune response. Here, we describe the protective and immunomodulating properties of an influenza vector FluVec-N carrying the C-terminal fragment of the SARS-CoV-2 nucleoprotein within a truncated NS1 open reading frame. Methods: We generated several FluVec-N recombinant vectors by reverse genetics and confirmed the vector's genetic stability, antigen expression in vitro, attenuation, and immunogenicity in a mouse model. We tested the protective potential of FluVec-N intranasal immunization in naïve mice and seropositive Th2-prone mice, primed with aluminium-adjuvanted inactivated SARS-CoV-2. Immune response in immunized and challenged mice was analyzed through serological methods and flow cytometry. Results: Double intranasal immunization of naïve mice with FluVec-N reduced weight loss and viral load in the lungs following infection with the SARS-CoV-2 beta variant. Mice primed with alum-adjuvanted inactivated coronavirus experienced substantial early weight loss and eosinophilia in the lungs during infection, demonstrating signs of enhanced disease. A single intranasal boost immunization with FluVec-N prevented the disease enhancement in primed mice by modulating the local immune response. Protection was associated with the formation of specific IgA and the early activation of virus-specific effector and resident CD8+ lymphocytes in mouse lungs. Conclusions: Our study supports the potential of immunization with influenza vector vaccines to prevent respiratory diseases and associated immunopathology.

A Systematic Review of the Distribution and Prevalence of Viruses Detected in the Peromyscus maniculatus Species Complex (Rodentia: Cricetidae)

The North American Deermouse, Peromyscus maniculatus, is one of the most widespread and abundant mammals on the continent. It is of public health interest as a known host of several viruses that are transmissible to humans and can cause illness, including the acute respiratory disease Hantavirus pulmonary syndrome (HPS). However, recent taxonomic studies indicate that P. maniculatus is a complex of multiple species, raising questions about how to identify and interpret three decades of hantavirus monitoring data. We conducted a systematic review investigating the prevalence and spatial distribution of viral taxa detected in wild populations allocated to P. maniculatus. From the 49 relevant studies published from 2000 to 2022, we extracted and analyzed spatial occurrence data to calculate weighted populational prevalences for hantaviruses. We found that detection efforts have been concentrated in the Western United States and Mexico with a focus on the spread of Sin Nombre virus (Orthohantavirus sinnombreense), the primary causative agent of HPS. There are significant gaps in the existing literature both geographically and in regard to the types of viruses being sampled. These results are significantly impacted by a recent taxonomic split of P. maniculatus into four species, and we were able to update 94% of hantavirus observations to reflect this change. Investigating the uncertain, and likely multiple, phylogenetic histories of these viral hosts should be a key emphasis of future modeling efforts.

Three-year seroprevalence of SARS-CoV-2 nucleocapsid protein antibody among children, parental awareness, and contributors of infection: a single-school cohort study in Chiba, Japan

BACKGROUND

Coronavirus disease 2019 (COVID-19) in children is often asymptomatic, posing challenges in detecting infections. Additionally, factors contributing to infection remain poorly understood. This study aimed to investigate trends in anti-severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) nucleocapsid antibody seroprevalence, the relationship between seroprevalence and parental perception of child infection, and factors related to COVID-19 in children.

METHODS

In December 2020, 355 children aged 6-12 years in one elementary school were enrolled in the study. The anti-SARS-CoV-2 nucleocapsid antibody seroprevalence was assessed, and questionnaires were administered annually for three years. Parents' perceptions of infection and factors contributing to infection were examined.

RESULTS

The seroprevalence was 0.6%, 2.2%, and 60.9% in the first, second, and third years, respectively. The third-year seroprevalence among children reported as 'infected,' 'not tested but had symptoms,' and 'not infected' by parents was 97.3%, 83.3%, and 35.7%, respectively. Increased odds of seropositivity at the third-year measurement were observed in lower grades (adjusted odds ratio [aOR]=2.79 compared with higher grades) and in children more likely to play with others (aOR=3.97 for 'somewhat' and 2.84 for 'often,' compared with 'rarely'). No significant associations with seropositivity were found for sex, siblings, body mass index, serum 25-OH vitamin D3 concentration, or sleep duration.

CONCLUSION

The Omicron variant outbreak from the end of 2021 led to a sharp increase in seroprevalence among children, with many unaware of their infection. Frequent play with others may facilitate transmission in children. These data provide useful information for developing countermeasures against COVID-19 and other future pandemics.

Higher Post-Acute Health Care Costs Following SARS-CoV-2 Infection Among Adults in Ontario, Canada

Purpose and Introduction

Growing evidence suggests SARS-CoV-2 infection increases the risk of long term cardiovascular, neurological, and other effects. However, post-acute health care costs following SARS-CoV-2 infection are not known.

Patients and Statistical Methods

Beginning 56 days following SARS-CoV-2 polymerase chain reaction (PCR) testing, we compared person-specific total and component health care costs (2020 CAD$) for the first year of follow-up at the mean and 99th percentiles of health care costs for matched test-positive and test-negative adults in Ontario, Canada, between January 1, 2020, and March 31, 2021. Matching included demographics, baseline clinical characteristics, and two-week time blocks.

Results

For 531,182 people, mean person-specific total health care costs were $513.83 (95% CI $387.37-$638.40) higher for test-positive females and $459.10 (95% CI $304.60-$615.32) higher for test-positive males, which were driven by hospitalization, long-term care, and complex continuing care costs. At the 99th percentile of each subgroup, person-specific health care costs were $12,533.00 (95% CI $9008.50-$16,473.00) higher for test-positive females and $14,604.00 (95% CI $9565.50-$19,506.50) for test-positive males, driven by hospitalization, specialist (males), and homecare costs (females). Cancer costs were lower. Six-month and 1-year cost differences were similar.

Conclusion

Post-acute health care costs after a positive SARS-CoV-2 PCR test were significantly higher than matched test-negative individuals, and these increased costs persisted for at least one year. The largest increases health care costs came from hospitalizations, long-term care, complex continuing care, followed by outpatient specialists (for males) and homecare costs (for women). Given the magnitude of ongoing viral spread, policymakers, clinicians, and patients should be aware of higher post-acute health care costs following SARS-CoV-2 infection.

Infection episodes and islet autoantibodies in children at increased risk for type 1 diabetes before and during the COVID-19 pandemic

OBJECTIVES

To determine the impact of the COVID-19 pandemic on the incidence rates of infection and islet autoimmunity in children at risk for type 1 diabetes.

METHODS

1050 children aged 4 to 7 months with an elevated genetic risk for type 1 diabetes were recruited from Germany, Poland, Sweden, Belgium and the UK. Reported infection episodes and islet autoantibody development were monitored until age 40 months from February 2018 to February 2023.

RESULTS

The overall infection rate was 311 (95% Confidence Interval [CI], 304-318) per 100 person years. Infection rates differed by age, country, family history of type 1 diabetes, and period relative to the pandemic. Total infection rates were 321 per 100 person-years (95% CI 304-338) in the pre-pandemic period (until February 2020), 160 (95% CI 148-173) per 100 person-years in the first pandemic year (March 2020-February 2021; P < 0.001) and 337 (95% CI 315-363) per 100 person-years in subsequent years. Similar trends were observed for respiratory and gastrointestinal infections. Islet autoantibody incidence rates were 1.6 (95% CI 1.0-2.4) per 100 person-years in the pre-pandemic period, 1.2 (95% CI 0.8-1.9) per 100 person-years in the first pandemic year (P = 0.46), and 3.4 (95% CI 2.3-4.8) per 100 person-years in subsequent years (P = 0.005 vs. pre-pandemic year; P < 0.001 vs. first pandemic year).

CONCLUSIONS

The COVID-19 pandemic was associated with significantly altered infection patterns. Islet autoantibody incidence rates increased two-fold when infection rates returned to pre-pandemic levels.

COVID-19 Vaccination Recommendations for 2024-2025 in Korea

The Korean Society of Infectious Diseases has been regularly publishing guidelines for adult immunization since 2007. Following the release of coronavirus disease 2019 (COVID-19) vaccination recommendations in 2023, significant changes have occurred due to the emergence of new variant strains and the waning immunity from previous vaccinations. This article provides a comprehensive update as of November 2024, incorporating the latest evidence and guidelines. Focusing on the 2024-2025 season, this article reviews vaccines currently authorized in Korea and assesses their effectiveness against the predominant JN.1 lineage variants. The updated recommendations prioritize high-risk groups, including adults aged 65 and older, individuals with underlying medical conditions, residents of facilities vulnerable to infection, pregnant women, and healthcare workers, for vaccination with updated vaccines targeting the JN.1 strain. Additionally, COVID-19 vaccination is available for all individuals aged 6 months and older. For most adults, a single-dose strategy is emphasized, while tailored schedules may be recommended for immunocompromised individuals. This update aims to optimize vaccination strategies in Korea to ensure comprehensive protection for high-risk populations.

Factors Predicting COVID-19 Vaccine Effectiveness and Longevity of Humoral Immune Responses

The COVID-19 pandemic, caused by SARS-CoV-2, prompted global efforts to develop vaccines to control the disease. Various vaccines, including mRNA (BNT162b2, mRNA-1273), adenoviral vector (ChAdOx1, Ad26.COV2.S), and inactivated virus platforms (BBIBP-CorV, CoronaVac), elicit high-titer, protective antibodies against the virus, but long-term antibody durability and effectiveness vary. The objective of this study is to elucidate the factors that influence vaccine effectiveness (VE) and the longevity of humoral immune responses to COVID-19 vaccines through a review of the relevant literature, including clinical and real-world studies. Here, we discuss the humoral immune response to different COVID-19 vaccines and identify factors influencing VE and antibody longevity. Despite initial robust immune responses, vaccine-induced immunity wanes over time, particularly with the emergence of variants, such as Delta and Omicron, that exhibit immune escape mechanisms. Additionally, the durability of the humoral immune responses elicited by different vaccine platforms, along with the identification of essential determinants of long-term protection-like pre-existing immunity, booster doses, hybrid immunity, and demographic factors-are critical for protecting against severe COVID-19. Booster vaccinations substantially restore neutralizing antibody levels, especially against immune-evasive variants, while individuals with hybrid immunity have a more durable and potent immune response. Importantly, comorbidities such as diabetes, cardiovascular disease, chronic kidney disease, and cancer significantly reduce the magnitude and longevity of vaccine-induced protection. Immunocompromised individuals, particularly those undergoing chemotherapy and those with hematologic malignancies, have diminished humoral responses and benefit disproportionately from booster vaccinations. Age and sex also influence immune responses, with older adults experiencing accelerated antibody decline and females generally exhibiting stronger humoral responses compared to males. Understanding the variables affecting immune protection is crucial to improving vaccine strategies and predicting VE and protection against COVID-19.

Neutralizing antibody correlate of protection against severe-critical COVID-19 in the ENSEMBLE single-dose Ad26.COV2.S vaccine efficacy trial

Assessment of immune correlates of severe COVID-19 has been hampered by the low numbers of severe cases in COVID-19 vaccine efficacy (VE) trials. We assess neutralizing and binding antibody levels at 4 weeks post-Ad26.COV2.S vaccination as correlates of risk and of protection against severe-critical COVID-19 through 220 days post-vaccination in the ENSEMBLE trial (NCT04505722), constituting ~4.5 months longer follow-up than our previous correlates analysis and enabling inclusion of 42 severe-critical vaccine-breakthrough cases. Neutralizing antibody titer is a strong inverse correlate of severe-critical COVID-19, with estimated hazard ratio (HR) per 10-fold increase 0.35 (95% CI: 0.13, 0.90). In a multivariable model, HRs are 0.31 (0.11, 0.89) for neutralizing antibody titer and 1.22 (0.49, 3.02) for anti-Spike binding antibody concentration. VE against severe-critical COVID-19 rises with neutralizing antibody titer: 63.1% (95% CI: 40.0%, 77.3%) at unquantifiable [<4.8975 International Units (IU)50/ml], 85.2% (47.2%, 95.3%) at just-quantifiable (5.2 IU50/ml), and 95.1% (81.1%, 96.9%) at 90th percentile (30.2 IU50/ml). At the same titers, VE against moderate COVID-19 is 32.5% (11.8%, 48.4%), 33.9% (19.1%, 59.3%), and 60.7% (40.4%, 76.4%). Protection against moderate vs. severe disease may require higher antibody levels, and very low antibody levels and/or other immune responses may associate with protection against severe disease.

SARS-CoV-2 seroprevalence and associated factors among outpatient attendees at health facilities in different provinces in Chad

BACKGROUND

Chad with 7,698 confirmed cases of infection and 194 deaths since the beginning of the COVID-19 pandemic, is one of the African countries with the lowest reported case numbers. However, this figure likely underestimates the true spread of the virus due to the low rate of diagnosis. The high rate of asymptomatic infections reflects the reality of SARS-CoV-2 transmission in Chad. In this study, we estimated the seroprevalence and identified factors associated with SARS-CoV-2 infection.

METHODS

A cross-sectional study was conducted between September 2022 and February 2023. A total of 1,290 plasma samples were collected from outpatient attendees at Health Facilities located in 11 provinces of Chad and tested by ELISA method, for the presence of IgG antibodies to SARS-CoV2 nucleocapsid (N) protein. KoboToolbox was used to gather data from the participants and data were analyzed using STATA 16.

RESULTS

The overall seroprevalence was 83.0% [95% CI = 81.6%-85.5%], with variations between provinces, ranging from 99.2% [95% CI = 94.0%-100%] in Moundou (Southern Chad) to 46.8% [95% CI = 36.0% -57.1%] in Biltine (Eastern Chad). Factors associated with the seroprevalence included military occupation (OR = 0.37 CI [0.80-1.77] p = 0.025) and age group between 55-64 years (OR = 0.33 CI [0.15-0.72] p = 0.005). While, other factors, such as gender and age were not significantly associated with seroprevalence.

CONCLUSION

Our results indicated that, the seroprevalence of COVID-19 in Chad is among the highest in Sub-Saharan Africa. These estimates could guide the response and public health policy decisions, enhancing the management of future outbreaks involving respiratory pathogens.

High immunity and low mortality after Omicron and mass event in Cameroon despite low vaccination

Background

Little is known about the evolution of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) immunity in African communities.

Aim

We evaluated changes in anti-SARS-CoV-2 antibodies, mortality and vaccination status in Cameroon between August 2021 and September 2022 to begin describing the evolution of the pandemic in Africa.

Setting

The study was conducted across Cameroon's 10 regional capitals, between 2021 and 2022 as the country hosted a mass gathering.

Methods

We conducted a cross-sectional population-based survey in 2022, including SARS-CoV-2 seroprevalence testing and retrospective mortality estimation using two-stage cluster sampling. We estimated and compared seroprevalence and crude mortality rates (CMR) to a survey conducted in 2021 using the same methodology.

Results

We performed serologic testing on 8400 individuals and collected mortality data from 22 314 individuals. Approximately 5% in each survey reported SARS-CoV-2-vaccination. Rapid diagnostic test-based seroprevalence increased from 11.2% (95% confidence interval [CI]: 10-12.5) to 59.8% (95% CI: 58.3-61.2) between 2021 and 2022, despite no increase in the proportion vaccinated. The CMR decreased from 0.17 to 0.06 deaths per 10 000 persons per day between 2021 and 2022. In 2022, no deaths were reportedly attributable to COVID-19 as compared to 17 deaths in 2021.

Conclusion

Over a 12-month period encompassing two waves of omicron variant SARS-CoV-2 and a mass gathering, SARS-CoV-2 seropositivity in Cameroon approached 60%, and deaths declined despite low vaccination coverage.

Contribution

This study challenges the assumption that high immunisation coverage is the sole determinant of epidemic control in the African context and encourages policymakers to increasingly rely on local research when designing response strategies for more effective outbreak management.

Reconstructing the age-structured case count of COVID-19 from sentinel surveillance data in Japan: A modeling study

OBJECTIVES

To reconstruct age-structured case counts of COVID-19 using sentinel reporting, which replaced universal reporting of COVID-19 from May 2023 in Japan.

METHODS

Using COVID-19 sentinel data stratified by discrete age groups in selected prefectures and referring to universal case count data up to May 8, 2023, we fitted a statistical model to handle weekly growth rates as a function of age and time so as to convert sentinel data to case counts after cessation of universal reporting.

RESULTS

The age distribution of cases in sentinel reporting was significantly biased toward younger age groups compared to universal reporting. When comparing the epidemic size of the 9th wave (May 8 to September 18, 2023) to the 8th wave (October 3, 2022 to April 10, 2023), using the wave-on-wave ratio of total cumulative sentinel cases led to a significant underestimation of the wave-on-wave in Tokyo (0.975, vs 1.461 by universal reporting) and Okinawa (1.299, vs 1.472). The estimates of growth rates, scaling factors between universal and sentinel cases, and expected universal case count showed robustness to changes in the ending week of the data period.

CONCLUSION

Our model quantified COVID-19 dynamics, comparably to universal reporting that ended in May 2023, enabling detailed and up-to-date health burden analysis using sentinel reports. The cumulative incidence was greater than that suggested from sentinel data in Tokyo, Nara, and Okinawa. Per-population burdens among children were particularly high in Osaka and Nara, indicating a strong bias in sentinel reporting toward pediatric cases.

A SARS-CoV-2 minimum data standard to support national serology reporting

BACKGROUND

Healthcare laboratory systems produce and capture a vast array of information, yet do not always report all of this to the national infrastructure within the United Kingdom. The global COVID-19 pandemic brought about a much greater need for detailed healthcare data, one such instance being laboratory testing data. The reporting of qualitative laboratory test results (e.g. positive, negative or indeterminate) provides a basic understanding of levels of seropositivity. However, to better understand and interpret seropositivity, how it is determined and other factors that affect its calculation (i.e. levels of antibodies), quantitative laboratory test data are needed.

METHOD

36 data attributes were collected from 3 NHS laboratories and 29 CO-CONNECT project partner organisations. These were assessed against the need for a minimum dataset to determine data attribute importance. An NHS laboratory feasibility study was undertaken to assess the minimum data standard, together with a literature review of national and international data standards and healthcare reports.

RESULTS

A COVID serology minimum data standard (CSMDS) comprising 12 data attributes was created and verified by 3 NHS laboratories to allow national granular reporting of COVID serology results. To support this, a standardised set of vocabulary terms was developed to represent laboratory analyser systems and laboratory information management systems.

CONCLUSIONS

This paper puts forward a minimum viable standard for COVID-19 serology data attributes to enhance its granularity and augment the national reporting of COVID-19 serology laboratory results, with implications for future pandemics.

Seroprevalence of SARS-CoV-2 antibodies among healthy blood donors: a systematic review and meta-analysis

INTRODUCTION

The development of a potent immune response and antibodies against SARS-CoV-2 is important for herd immunity. The serological response may be due to a previous infection or vaccination. Healthy blood donors could represent and provide information on the immune status of the general population. Therefore, we estimated the global and regional prevalence of SARS-CoV-2 antibodies among healthy blood donors.

METHODS

We conducted a systematic search of PubMed, Scopus, and ProQuest from December 2019 to January 2023. After critical appraisal and quality assessment, a qualitative synthesis of the identified relevant articles was performed. The random-effects model was used to estimate the pooled prevalence of SARS-CoV-2 antibodies. Funnel plots and Egger's test were used to assess publication bias. Sensitivity analysis was performed, and heterogeneity was quantified using I2 statistics.

RESULTS

A total of 70 peer-reviewed articles were selected that together included 2,454,192 blood donors. The global estimated pooled prevalence of SARS-CoV-2 antibodies among healthy blood donors was 10.3% (95% CI: 4.6 - 18.0%, n = 70). The highest seroprevalence was observed in Asia (17.7%), followed by Africa (16.1%). The seroprevalence in studies conducted before the introduction of the vaccine was 6.1%, whereas those of studies conducted after vaccines were available was 27.6%. High seroprevalence was observed in studies that measured antibodies against the S protein of the virus (15.2%), while lower (12.5%) in those that measured antibodies against the N protein. A high seroprevalence was observed in studies that only measured IgG antibodies (16.3%), and it was 5.9% in studies that measured total antibodies.

CONCLUSION

The prevalence of SARS-CoV-2 antibodies among healthy blood donors varies, potentially indicating geographical disparities in transmission and vaccination rates. To enhance community resilience, addressing these differences through inclusive health policies and adaptable public health measures is crucial.

School mask policies and SARS-CoV-2 seroprevalence among school-age children-United States, September to December 2021

During September to December 2021, school mask policies to mitigate SARS-CoV-2 transmission varied throughout the US. We compared infection-induced seroprevalence estimates and estimated seroconversion among children residing in areas with and without school mask requirements. We estimated infection-induced seroprevalence among children in three age groups (5-17, 5-11, and 12-17 years) in areas with and without school district mask requirements for two time points: September 1-30, 2021 and December 15, 2021 to January 14, 2022. Robust Poisson regression models estimated population seroconversion over the semester among initially seronegative children. Permutation tests assessed for significant differences in the estimated population seroconversion due to incident infections by school district mask policy. Residing in an area with no school mask requirement was associated with higher infection-induced seroprevalence among children aged 5-17 years (adjusted prevalence ratio [aPR] = 1.18, 95% confidence interval [CI]: 1.10, 1.26), and those aged 5-11 years (aPR) = 1.21, 95% CI: 1.10, 1.32) and those aged 12-17 years (aPR = 1.16, 95% CI: 1.07, 1.26), compared with areas requiring masks in school. Estimated population seroconversion during the semester was also significantly higher among children in districts without mask policies than those with school mask requirements among all age groups (5-17 years: 23.7% vs 18.1%, P < 0.001; 5-11 years: 6.4% vs 4.5%, P = 0.002;12-17 years: 27.2% vs 21.0%, P < 0.001). During the U.S. Fall 2021 semester, areas with school mask requirements had lower infection-induced seroprevalence and an estimated lower proportion of seroconversion due to incident infection among school-aged children compared with areas without school mask requirements; causality cannot necessarily be inferred from these associations.

IMPORTANCE

During the U.S. Fall 2021 school semester, the estimated proportion of previously uninfected school-aged children who experienced a first infection with SARS-CoV-2 was lower in areas where public school district policies required masks for all staff and students compared with areas where the school districts had no mask requirements. Because children are more likely than adults to experience asymptomatic or mild SARS-CoV-2 infections, the presence of infection-induced antibodies is a more accurate measure of infection history than clinical testing. The proportion of children with these antibodies (i.e., seroprevalence) can improve our understanding of SARS-CoV-2 by detecting more infections and eliminating potential bias due to local testing and reporting practices. Enhanced robustness of surveillance for respiratory infections in children, including records of mitigation policies in communities and schools, as well as seroprevalence data, would establish a better evidence base for policy decisions and response measures during future respiratory outbreaks.

Mosaic sarbecovirus nanoparticles elicit cross-reactive responses in pre-vaccinated animals

Immunization with mosaic-8b (nanoparticles presenting 8 SARS-like betacoronavirus [sarbecovirus] receptor-binding domains [RBDs]) elicits more broadly cross-reactive antibodies than homotypic SARS-CoV-2 RBD-only nanoparticles and protects against sarbecoviruses. To investigate original antigenic sin (OAS) effects on mosaic-8b efficacy, we evaluated the effects of prior COVID-19 vaccinations in non-human primates and mice on anti-sarbecovirus responses elicited by mosaic-8b, admix-8b (8 homotypics), or homotypic SARS-CoV-2 immunizations, finding the greatest cross-reactivity for mosaic-8b. As demonstrated by molecular fate mapping, in which antibodies from specific cohorts of B cells are differentially detected, B cells primed by WA1 spike mRNA-LNP dominated antibody responses after RBD-nanoparticle boosting. While mosaic-8b- and homotypic-nanoparticles boosted cross-reactive antibodies, de novo antibodies were predominantly induced by mosaic-8b, and these were specific for variant RBDs with increased identity to RBDs on mosaic-8b. These results inform OAS mechanisms and support using mosaic-8b to protect COVID-19-vaccinated/infected humans against as-yet-unknown SARS-CoV-2 variants and animal sarbecoviruses with human spillover potential.

SARS-CoV-2 correlates of protection from infection against variants of concern

Serum neutralizing antibodies (nAbs) induced by vaccination have been linked to protection against symptomatic and severe coronavirus disease 2019. However, much less is known about the efficacy of nAbs in preventing the acquisition of infection, especially in the context of natural immunity and against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) immune-escape variants. Here we conducted mediation analysis to assess serum nAbs induced by prior SARS-CoV-2 infections as potential correlates of protection against Delta and Omicron infections, in rural and urban household cohorts in South Africa. We find that, in the Delta wave, D614G nAbs mediate 37% (95% confidence interval: 34-40%) of the total protection against infection conferred by prior exposure to SARS-CoV-2, and that protection decreases with waning immunity. In contrast, Omicron BA.1 nAbs mediate 11% (95% confidence interval: 9-12%) of the total protection against Omicron BA.1 or BA.2 infections, due to Omicron's neutralization escape. These findings underscore that correlates of protection mediated through nAbs are variant specific, and that boosting of nAbs against circulating variants might restore or confer immune protection lost due to nAb waning and/or immune escape. However, the majority of immune protection against SARS-CoV-2 conferred by natural infection cannot be fully explained by serum nAbs alone. Measuring these and other immune markers including T cell responses, both in the serum and in other compartments such as the nasal mucosa, may be required to comprehensively understand and predict immune protection against SARS-CoV-2.

Pandemic burden in low-income settings and impact of limited and delayed interventions: A granular modelling analysis of COVID-19 in Kabwe, Zambia

OBJECTIVES

Pandemic response in low-income countries (LICs) or settings often suffers from scarce epidemic surveillance and constrained mitigation capacity. The drivers of pandemic burden in such settings, and the impact of limited and delayed interventions remain poorly understood.

METHODS

We analysed COVID-19 seroprevalence and all-cause excess deaths data from the peri-urban district of Kabwe, Zambia between March 2020 and September 2021 with a novel mathematical model. Data encompassed three consecutive waves caused by the wild-type, Beta and Delta variants.

RESULTS

Across all three waves, we estimated a high cumulative attack rate, with 78% (95% credible interval [CrI] 71-85) of the population infected, and a high all-cause excess mortality, at 402 (95% CrI 277-473) deaths per 100,000 people. Ambitiously improving health care to a capacity similar to that in high-income settings could have averted up to 46% (95% CrI 41-53) of accrued excess deaths, if implemented from June 2020 onward. An early and accelerated vaccination rollout could have achieved the highest reductions in deaths. Had vaccination started as in some high-income settings in December 2020 and with the same daily capacity (doses per 100 population), up to 68% (95% CrI 64-71) of accrued excess deaths could have been averted. Slower rollouts would have still averted 62% (95% CrI 58-68), 54% (95% CrI 49-61) or 26% (95% CrI 20-38) of excess deaths if matching the average vaccination capacity of upper-middle-, lower-middle- or LICs, respectively.

CONCLUSIONS

Robust quantitative analyses of pandemic data are of pressing need to inform future global pandemic preparedness commitments.

Impact of cross-reactivity and herd immunity on SARS-CoV-2 pandemic severity

Public health systems reported low mortality from severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in East Asia, in low-income countries, and for children during the first year of the SARS-CoV-2 pandemic. These reports led commentators to suggest that cross-reactive immunity from prior exposure to other pathogens reduced fatality risk. Resolution of initial infection waves also contributed to speculation that herd immunity prevented further waves prior to vaccination. Serology instead implied that immunity was too limited to achieve herd immunity and that there was little impact from cross-reactive protection. Paediatric deaths exceeded those from influenza, with higher age-specific fatality risk in lower-income nations and similar fatality risk in East Asia compared with demographically similar regions. Neither pre-outbreak exposure to related pathogens nor immunity induced by initial infection waves are necessarily a reliable response to future pathogen outbreaks. Preparedness for future pathogen outbreaks should instead focus on strategies such as voluntary behavioural changes, nonpharmaceutical interventions, and vaccination.

Immunogenicity and Safety of Omicron-Containing Multivalent COVID-19 Vaccines in Unvaccinated and Previously Vaccinated Adults

The SARS-CoV-2 evolution trajectory remains uncertain, and the antigenic characteristics of future variants are highly unpredictable. We report the immunogenicity and safety of multivalent COVID-19 vaccines, SCTV01E and SCTV01E-1, against Omicron BA.5. This phase 2 trial randomized 400 adults into two cohorts, 160 unvaccinated (3 doses) and 240 previously vaccinated (2 doses) individuals to receive 30 µg SCTV01E-1 or 30 µg SCTV01E (1:1) between 4 November and 28 November 2022. Among the unvaccinated cohort, day 42 geometric mean fold rises (GMFRs) of neutralizing antibodies (nAb) against Omicron BA.5 were reported to be 12.8× and 20.5× over day 0 for SCTV01E-1 and SCTV01E, respectively. On day 178, both vaccines increased geometric mean titers (GMTs) of nAb against BA.5 following the booster dose compared to pre-booster levels on D150. Similar frequencies of solicited [6.2% (5/81) and 7.6% (6/79)] and unsolicited [11.1% (9/81) and 10.1% (8/79)] adverse events (AEs) were reported in SCTV01E-1 and SCTV01E groups, respectively. Grade 3 or more AEs were < 2% in both vaccine groups [SCTV01E-1: 1.2% (1/81), SCTV01E: 1.3% (1/79)]. In the previously vaccinated cohort, similar GMFRs were reported on day 28 (SCTV01E-1: 9.4× and SCTV01E: 8.7×) over baseline (D0). On day 148, both vaccines showed increased nAb levels with similar GMFRs over D120. Comparable incidences of solicited [13.2% (16/121) and 10.9% (13/119)] and unsolicited [17.4% (21/121) and 10.9% (13/119)] AEs were reported in SCTV01E-1 and SCTV01E groups, respectively. Numerically identical ≥ grade 3 AEs [SCTV01E-1: 1.7% (2/121) and SCTV01E: 1.7% (2/119)] were reported. This trial demonstrates the effectiveness of updated multivalent vaccines with acceptable safety profiles.

Omicron COVID-19 immune correlates analysis of a third dose of mRNA-1273 in the COVE trial

In the phase 3 Coronavirus Efficacy (COVE) trial (NCT04470427), post-dose two Ancestral Spike-specific binding (bAb) and neutralizing (nAb) antibodies were shown to be correlates of risk (CoR) and of protection against Ancestral-lineage COVID-19 in SARS-CoV-2 naive participants. In the SARS-CoV-2 Omicron era, Omicron subvariants with varying degrees of immune escape now dominate, seropositivity rates are high, and booster doses are administered, raising questions on whether and how these developments affect the bAb and nAb correlates. To address these questions, we assess post-boost BA.1 Spike-specific bAbs and nAbs as CoRs and as correlates of booster efficacy in COVE. For naive individuals, bAbs and nAbs inversely correlate with Omicron COVID-19: hazard ratios (HR) per 10-fold marker increase (95% confidence interval) are 0.16 (0.03, 0.79) and 0.31 (0.10, 0.96), respectively. In non-naive individuals the analogous results are similar: 0.15 (0.04, 0.63) and 0.28 (0.07, 1.08). For naive individuals, three vs two-dose booster efficacy correlates with predicted nAb titer at exposure, with estimates -8% (-126%, 48%), 50% (25%, 67%), and 74% (49%, 87%), at 56, 251, and 891 Arbitrary Units/ml. These results support the continued use of antibody as a surrogate endpoint.

High SARS-CoV-2 seroincidence but low excess COVID mortality in Sierra Leone in 2020-2022

While SARS-CoV-2 infection appears to have spread widely throughout Africa, documentation of associated mortality is limited. We implemented a representative serosurvey in one city of Sierra Leone in Western Africa, paired with nationally representative mortality and selected death registration data. Cumulative seroincidence using high quality SARS-CoV-2 serological assays was 69% by July 2021, rising to 84% by April 2022, mostly preceding SARS-CoV-2 vaccination. About half of infections showed evidence of neutralizing antibodies. However, excess death rates were low, and were concentrated at older ages. During the peak weeks of viral activity, excess mortality rates were 22% for individuals aged 30-69 years and 70% for those over 70. Based on electronic verbal autopsy with dual independent physician assignment of causes, excess deaths during viral peaks from respiratory infections were notable. Excess deaths differed little across specific causes that, a priori, are associated with COVID, and the pattern was consistent among adults with or without chronic disease risk factors. The overall 6% excess of deaths at ages ≥30 from 2020-2022 in Sierra Leone is markedly lower than reported from South Africa, India, and Latin America. Thus, while SARS-CoV-2 infection was widespread, our study highlights as yet unidentified mechanisms of heterogeneity in susceptibility to severe disease in parts of Africa.

Prevalence of SARS-CoV-2 Antibodies in Kosovo-Wide Population-Based Seroepidemiological Study

BACKGROUND

Seroprevalence studies have proven to be an important tool in tracking the progression of the coronavirus disease 2019 (COVID-19) pandemic. The aim of this study was to measure the seroprevalence of antibodies to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in the general population of Kosovo by gender, age group and region and among asymptomatic people.

METHOD

The Institute of Public Health of Kosovo conducted a cross-sectional population-based survey, aligned with the protocols of the WHO Unity Studies, from the beginning of May to the end of June 2021.

RESULTS

The survey covered a total of 2204 people with a response rate of 91.8% (41.9% [923] males and 51.2% [1281] females). In May to June 2021, the prevalence of antibodies in the overall population (IgG antibodies ≥ 1.1) was 37.0%. Seroprevalence was 34.4% in men and 38.9% in women (p < 0.05), with the highest percentage (48.7%) found in the 60-69 years' age group. The overall prevalence of acute IgM antibodies (IgM ≥ 1.1) was 1% (95% CI: 0.7%-1.5%), with no significant difference between genders and the highest prevalence among participants of 60-69 years of age (1.6%; 95% CI: 0.7%-3.6%).

CONCLUSION

A high prevalence of antibodies against SARS-CoV-2 was found in Kosovo before the start of the vaccination campaign. However, the results of the survey suggested that, by the end of June 2021, a desirable level of protection from the SARS-CoV-2 virus had not been reached.

Post-Omicron SARS-CoV-2 serostatus in Sierra Leone: A cross-sectional study in a maternity hospital setting in Freetown, November/December 2022

BACKGROUND

Spread of SARS-CoV-2 in Sub-Saharan African countries has been poorly investigated, especially in the later pandemic stages. We aimed to assess the post-Omicron situation in Sierra Leone in November/December 2022 considering SARS-CoV-2 serostatus, vaccinations, and behavioral factors.

METHODS

In a cross-sectional study conducted in a maternity hospital in Freetown, Sierra Leone, both patients and staff provided dried blood spot samples for analysis of anti-S and anti-N IgG prevalence using Anti-SARS-CoV-2-ELISA. Additionally, we collected sociodemographic and infection-related information through questionnaires. Outcome parameters included seropositivity, infection-related seroprevalence, and self-reported vaccination status. We used logistic regression to identify associations with prior infection and with vaccination status.

RESULTS

Out of 791 participants (389 patients, 402 staff), 670 (84.7 %) displayed a positive SARS-CoV-2 serostatus resulting from either infection or vaccination. Among a sub-sample of 514 participants within which determination of prior natural infection was possible, 441individuals (85.8 %) were affected. Prior infection was associated with female sex and tertiary education level. Overall, 60.3 % reported having been vaccinated. Staff as opposed to patients, and individuals with higher socioeconomic status were more likely to report vaccination. Individuals who assessed their risk of COVID-19 as either higher or lower compared to a medium-level risk were more likely to have contracted the virus and less likely to have received vaccination.

CONCLUSION

Our findings suggest that since the Omicron wave in 2022, the Sierra Leonean population has almost universally been exposed to SARS-CoV-2. While this is encouraging in the light of relatively low excess mortality in the country, future investigations on the long-term effect of high viral exposure on epidemic resilience and public health impact will be crucial.

Surveillance bias in the assessment of the size of COVID-19 epidemic waves: a case study

OBJECTIVES

To estimate the size of COVID-19 waves using four indicators across three pandemic periods and assess potential surveillance bias.

STUDY DESIGN

Case study using data from one region of Switzerland.

METHODS

We compared cases, hospitalizations, deaths, and seroprevalence during three periods including the first three pandemic waves (period 1: Feb-Oct 2020; period 2: Oct 2020-Feb 2021; period 3: Feb-Aug 2021). Data were retrieved from the Federal Office of Public Health or estimated from population-based studies. To assess potential surveillance bias, indicators were compared to a reference indicator, i.e. seroprevalence during periods 1 and 2 and hospitalizations during the period 3. Timeliness of indicators (the duration from data generation to the availability of the information to decision-makers) was also evaluated.

RESULTS

Using seroprevalence (our reference indicator for period 1 and 2), the 2nd wave size was slightly larger (by a ratio of 1.4) than the 1st wave. Compared to seroprevalence, cases largely overestimated the 2nd wave size (2nd vs 1st wave ratio: 6.5), while hospitalizations (ratio: 2.2) and deaths (ratio: 2.9) were more suitable to compare the size of these waves. Using hospitalizations as a reference, the 3rd wave size was slightly smaller (by a ratio of 0.7) than the 2nd wave. Cases or deaths slightly underestimated the 3rd wave size (3rd vs 2nd wave ratio for cases: 0.5; for deaths: 0.4). The seroprevalence was not useful to compare the size of these waves due to high vaccination rates. Across all waves, timeliness for cases and hospitalizations was better than for deaths or seroprevalence.

CONCLUSIONS

The usefulness of indicators for assessing the size of pandemic waves depends on the type of indicator and the period of the pandemic.

Estimated number of lives directly saved by COVID-19 vaccination programmes in the WHO European Region from December, 2020, to March, 2023: a retrospective surveillance study

BACKGROUND

By March, 2023, 54 countries, areas, and territories (hereafter CAT) in the WHO European Region had reported more than 2·2 million COVID-19-related deaths to the WHO Regional Office for Europe. Here, we estimated how many lives were directly saved by vaccinating adults in the WHO European Region from December, 2020, to March, 2023.

METHODS

In this retrospective surveillance study, we estimated the number of lives directly saved by age group, vaccine dose, and circulating variant-of-concern (VOC) period, regionally and nationally, using weekly data on COVID-19 mortality and infection, COVID-19 vaccination uptake, and SARS-CoV-2 virus characterisations by lineage downloaded from The European Surveillance System on June 11, 2023, as well as vaccine effectiveness data from the literature. We included data for six age groups (25-49 years, 50-59 years, ≥60 years, 60-69 years, 70-79 years, and ≥80 years). To be included in the analysis, CAT needed to have reported both COVID-19 vaccination and mortality data for at least one of the four older age groups. Only CAT that reported weekly data for both COVID-19 vaccination and mortality by age group for 90% of study weeks or more in the full study period were included. We calculated the percentage reduction in the number of expected and reported deaths.

FINDINGS

Between December, 2020, and March, 2023, in 34 of 54 CAT included in the analysis, COVID-19 vaccines reduced deaths by 59% overall (CAT range 17-82%), representing approximately 1·6 million lives saved (range 1·5-1·7 million) in those aged 25 years or older: 96% of lives saved were aged 60 years or older and 52% were aged 80 years or older; first boosters saved 51% of lives, and 60% were saved during the Omicron period.

INTERPRETATION

Over nearly 2·5 years, most lives saved by COVID-19 vaccination were in older adults by first booster dose and during the Omicron period, reinforcing the importance of up-to-date vaccination among the most at-risk individuals. Further modelling work should evaluate indirect effects of vaccination and public health and social measures.

FUNDING

US Centers for Disease Control and Prevention.

COVID-19 IgG seropositivity and its determinants in occupational groups of varying infection risks in two Andean cities of Ecuador before mass vaccination

BACKGROUND

The COVID-19 pandemic has caused over 68.7 million infections and 1.35 million deaths in South America. There are limited data on SARS-CoV-2 seropositivity and its determinants from Andean countries prior to mass vaccinations against COVID-19.

OBJECTIVE

To estimate SARS-CoV-2 seropositivity and its determinants before vaccination in occupational groups of adults presumed to have different levels of exposure and associations with potential symptomatology.

METHODS

We measured seropositivity of anti-SARS-CoV-2 IgG antibodies in a cross-sectional study of vaccine-naïve adults aged 18 years and older, recruited within three occupational risk groups (defined as low [LR], moderate [MR], and high [HR]) between January and September 2021 in two Andean cities in Ecuador. Associations with risk factors were estimated using logistic regression.

RESULTS

In a sample of 882 adults, IgG seropositivity for the three different occupational risk groups was 39.9% (CI 95% 35.3-44.6), 74.6% (CI 95% 66.4-81.4), and 39.0% (CI 95% 34.0-44.4) for the HR, MR, and LR groups, respectively. History of an illness with loss of taste and/or smell was significantly associated with seropositivity in all occupational groups, with adjusted ORs of 14.31 (95%CI, 5.83-35.12; p<0.001), 14.34 (95%CI 3.01-68.42; p<0.001), and 8.79 (95%CI 2.69-28.72; p<0.001), for the HR, MR, and LR groups, respectively; while fever was significant for the LR group with an adjusted OR of 1.24 (95%CI, 1.11-4.57; p = 0.025) and myalgia for the HR group with an adjusted OR of 2.07 (95%CI, 1.13-3.81; p = 0.019).

CONCLUSION

Notable proportions of seropositivity were seen in all occupational groups between January and September 2021 prior to mass vaccination. Loss of taste and/or smell was strongly associated with presence of anti-SARS-CoV-2 IgG antibodies irrespective of presumed occupational exposure risk.

Seroprevalence trends of anti-SARS-CoV-2 antibodies in the adult population of the São Paulo Municipality, Brazil: Results from seven serosurveys from June 2020 to April 2022. The SoroEpi MSP Study

BACKGROUND

Sequential population-based household serosurveys of SARS-CoV-2 covering the COVID-19 pre- and post-vaccination periods are scarce in Brazil. This study investigated seropositivity trends in the municipality of São Paulo.

METHODS

We conducted seven cross-sectional surveys of adult population-representative samples between June 2020 and April 2022. The study design included probabilistic sampling, test for SARS-CoV-2 antibodies using the Roche Elecsys anti-nucleocapsid assay, and statistical adjustments for population demographics and non-response. The weighted seroprevalences with 95% confidence intervals (CI) were estimated by sex, age group, race, schooling, and mean income study strata. Time trends in seropositivity were assessed using the Joinpoint model. We compared infection-induced seroprevalences with COVID-19 reported cases in the pre-vaccination period.

RESULTS

The study sample comprised 8,134 adults. The overall SARS-CoV-2 seroprevalence increased from 11.4% (95%CI: 9.2-13.6) in June 2020 to 24.9% (95%CI: 21.0-28.7) in January 2021; from 38.1% (95%CI: 34.3-41.9) in April 2021 to 77.7% (95%CI: 74.4-81.0) in April 2022. The prevalence over time was higher in the subgroup 18-39 years old than in the older groups from Survey 3 onwards. The self-declared Black or mixed (Pardo) group showed a higher prevalence in all surveys compared to the White group. Monthly prevalence rose steeply from January 2021 onwards, particularly among those aged 60 years or older. The infection-to-case ratios ranged from 8.9 in June 2020 to 4.3 in January 2021.

CONCLUSIONS

The overall seroprevalence rose significantly over time and with age and race subgroup variations. Increases in the 60 years or older age and the White groups were faster than in younger ages and Black or mixed (Pardo) race groups in the post-vaccination period. Our data may add to the understanding of the complex and changing population dynamics of the SARS-CoV-2 infection, including the impact of vaccination strategies and the modelling of future epidemiological scenarios.

Overcoming Health Inequities: Spatial Analysis of Seroprevalence and Vaccination Against COVID-19 in Chile

Background

In unequal economies, the spread of the first waves of the COVID-19 was usually associated with low socioeconomic status of individuals and their families. Chile exemplified this. By mid-2020, Chile had one of the highest SARS-CoV-2 infection rates in the world predominantly in poorer areas. A year later, the country launched a universal vaccination campaign based on the national strategy of immunization established in 1975. By 2022, Chile presented one of the highest COVID-19 vaccination coverages globally, reaching 94.3% of the population with the primary scheme by the end of 2022.

Objective

This study analyzes the spatial distribution of SARS-CoV-2 seroprevalence at the beginning of the pandemic (2020) compared with the seroprevalence after 2 years of ongoing epidemic and COVID-19 vaccination campaigns (2022).

Methods

Two population-based random samples of individuals aged 7 years and older from two Chilean cities were studied. Utilizing an enzyme-linked immunosorbent assay test, IgG antibodies were measured in serum of 1061 participants in 2020, and 853 in 2022.

Results

Using the Global Moran's Index, the seroprevalence distribution pattern for the year 2020 showed clustering in the two cities. Conversely, seroprevalence and vaccinations were homogeneously distributed in 2022. These results show the success of the vaccination campaign in Chile, not only in coverage but also because it widely reached all individuals.

Conclusions

The uptake of this preventive measure is high, regardless of the social and economic factors, achieving broad population immunity. The extensive deployment of the primary health care network contributed to reducing health inequities and promoting to universal health access.

Characterization of the SARS-CoV-2 antibody landscape in Norway in the late summer of 2022: high seroprevalence in all age groups with patterns of primary Omicron infection in children and hybrid immunity in adults

BACKGROUND

According to Norwegian registries, 91% of individuals ≥ 16 years had received ≥ 1 dose of COVID-19 vaccine by mid-July 2022, whereas less than 2% of children < 12 years were vaccinated. Confirmed COVID-19 was reported for 27% of the population, but relaxation of testing lead to substantial underreporting. We have characterized the humoral immunity to SARS-CoV-2 in Norway in the late summer of 2022 by estimating the seroprevalence and identifying antibody profiles based on reactivity to Wuhan or Omicron-like viruses in a nationwide cross-sectional collection of residual sera, and validated our findings using cohort sera.

METHODS

1,914 anonymized convenience sera and 243 NorFlu-cohort sera previously collected from the Oslo-area with reported infection and vaccination status were analyzed for antibodies against spike, the receptor-binding domain (RBD) of the ancestral Wuhan strain and Omicron BA.2 RBD, and nucleocapsid (N). Samples were also tested for antibodies inhibiting RBD-ACE2 interaction. Neutralization assays were performed on subsets of residual sera against B.1, BA.2, XBB.1.5 and BQ.1.1.

RESULTS

The national seroprevalence estimate from vaccination and/or infection was 99.1% (95% CrI 97.0-100.0%) based on Wuhan (spike_W and RBD_W) and RBD_BA2 antibodies. Sera from children < 12 years had 2.2 times higher levels of antibodies against RBD_BA2 than RBD_W and their seroprevalence estimate showed a 14.4 percentage points increase when also including anti-RBD_BA2 antibodies compared to Wuhan-antibodies alone. 50.3% (95% CI 45.0-55.5%) of residual sera from children and 38.1% (95% CI 36.0-40.4%) of all residual sera were positive for anti-N-antibodies. By combining measurements of binding- and ACE2-RBD-interaction-inhibiting antibodies, reactivity profiles indicative of infection and vaccination history were identified and validated using cohort sera. Residual sera with a profile indicative of hybrid immunity were able to neutralize newer Omicron variants XBB.1.5 and BQ.1.1.

CONCLUSIONS

By late summer of 2022, most of the Norwegian population had antibodies to SARS-CoV-2, and almost all children had been infected. Antibody profiles indicated that children mostly had experienced a primary Omicron infection, while hybrid immunity was common among adults. The finding that sera displaying hybrid immunity could neutralize newer Omicron variants indicates that Wuhan-like priming of the immune response did not have a harmful imprinting effect and that infections induce cross-reacting antibodies against future variants.