Protective immunity of SARS-CoV-2 infection and vaccines against medically attended symptomatic omicron BA.4, BA.5, and XBB reinfections in Singapore: a national cohort study

Risk of reinfection and severity with the predominant BA.5 Omicron subvariant China, from December 2022 to January 2023

Data on reinfection in large Asian populations are limited. In this study, we aimed to evaluate the reinfection rate, disease severity, and time interval between the infections in the symptomatic and asymptomatic populations which are firstl infected with BA.2 Omicron Variant. We retrospectively included adult patients with COVID-19 discharged from four designated hospitals between 27 April 2021 and 30 November 2022, who were interviewed via telephone from 29 January to 1 March 2023. Univariable and multivariable analyses were used to explore risk factors associated with reinfection. A total of 16,558 patients were followed up, during the telephone survey of an average of 310.0 days, 1610 (9.72%) participants self-reported reinfection. The mean time range of reinfection was 257.9 days. The risks for reinfection were analysed using multivariable logistic regression. Patients with severe first infection were at higher risk for reinfection (aORs, 2.50; P < 0.001). The male (aORs,0.82; P < 0.001), the elderly (aORs, 0.44; P < 0.001), and patients with full vaccination (aORs, 0.67; P < 0.001) or booster (aORs, 0.63; P < 0.001) had the lower risk of reinfection. Patients over 60 years of age (aORs,9.02; P = 0.006) and those with ≥2 comorbidities (aORs,11.51; P = 0.016). were at higher risk for severe reinfection. The number of clinical manifestations of reinfection increases in people with severe first infection (aORs, 2.82; P = 0.023). The overall reinfection rate was 9.72%, and the reinfection rate of Omicron-to-Omicron subvariants was 9.50% at one year. The severity of Omicron-Omicron reinfection decreased. Data from our clinical study may provide clinical evidence and bolster response preparedness for future COVID-19 reinfection waves.

Neutralization sensitivity of SARS-CoV-2 Omicron variants FL.1 and GE.1 by therapeutic antibodies and XBB sera

Two SARS-CoV-2 XBB sub-variants, FL.1 and GE.1, have been increasing in prevalence worldwide, but limited information is available about their ability to evade the immune system. FL.1 and GE.1 are emerging Omicron XBB variants possessing additional mutations in the spike RBD raising concerns of increased neutralization escape. In this study, we assessed the neutralizing ability of eleven FDA-approved monoclonal antibody combinations against different Omicron variants, including BA.2.75, BA.2.76, BA.4/5, XBB.1.5, and CH.1.1. Among the eleven antibodies, Sotrovimab was the only antibody to show broad neutralization ability against XBB.1.5. However, Sotrovimab showed attenuated neutralization efficiency against recently emerging XBB sub-lineages EG.5, FL.1, and GE.1 compared to XBB.1.5. Additionally, XBB.1.5 seropositive convalescent sera displayed lower neutralization activity against EG.5, FL.1, and GE.1. Overall, our findings present enhanced immune evasion capacity of emerging XBB variants and emphasize the importance of continued monitoring of novel variants.

Factors associated with childhood non-vaccination against COVID-19 in Canada: A national survey analysis

Background

COVID-19 vaccination efforts are critical in mitigating the impact of the virus, but despite proven safety and efficacy, vaccination rates among children in Canada are lower than in adults, prompting a need to explore determinants of childhood COVID-19 non-vaccination to improve uptake.

Method

This study analyzed data from the Canadian COVID-19 Immunization Coverage Survey 2022. Using multivariable logistic regression, it examined the association between COVID-19 non-vaccination among children aged 5-17 and factors such as parental sociodemographic characteristics, vaccine knowledge, attitudes, and beliefs (KAB), and vaccination history.

Results

The analysis revealed that negative KAB towards vaccines, reflected in higher KAB composite scores, significantly increased the likelihood of non-vaccination. Additionally, factors such as lower household incomes, rural residence, employment in sectors not at risk for vaccine-preventable diseases, and younger parental age were associated with higher non-vaccination. The study also highlighted ethnic disparities in vaccination odds and found that children with incomplete routine vaccinations or inconsistent flu vaccination histories were more likely to be unvaccinated against COVID-19. Surprisingly, children of parents who consistently received flu vaccinations were more likely to be unvaccinated against COVID-19. Furthermore, parental education levels showed a complex relationship with children's COVID-19 vaccination status, indicating nuanced influences on vaccination decisions.

Conclusion

The findings offer vital insights into the factors influencing COVID-19 vaccination uptake among children in Canada, suggesting avenues for targeted strategies to improve vaccine coverage.

Susceptibility of healthcare personnel with severe acute respiratory coronavirus virus 2 (SARS-CoV-2) hybrid immunity to XBB lineage reinfection

Among 8,678 vaccinated healthcare personnel (HCP) with previous coronavirus disease 2019 (COVID-19), by August 28, 2023, 909 (10%) had an infection of severe acute respiratory coronavirus virus 2 (SARS-CoV-2) omicron XBB variant. Reinfection risk was comparable irrespective of previous infection type except for the omicron BQ.1 variant. Bivalent vaccination had a protective effect. COVID-19 vaccines remain vital to protect HCP, including those with hybrid immunity.

Imprinting of serum neutralizing antibodies by Wuhan-1 mRNA vaccines

Immune imprinting is a phenomenon in which prior antigenic experiences influence responses to subsequent infection or vaccination1,2. The effects of immune imprinting on serum antibody responses after boosting with variant-matched SARS-CoV-2 vaccines remain uncertain. Here we characterized the serum antibody responses after mRNA vaccine boosting of mice and human clinical trial participants. In mice, a single dose of a preclinical version of mRNA-1273 vaccine encoding Wuhan-1 spike protein minimally imprinted serum responses elicited by Omicron boosters, enabling generation of type-specific antibodies. However, imprinting was observed in mice receiving an Omicron booster after two priming doses of mRNA-1273, an effect that was mitigated by a second booster dose of Omicron vaccine. In both SARS-CoV-2-infected and uninfected humans who received two Omicron-matched boosters after two or more doses of the prototype mRNA-1273 vaccine, spike-binding and neutralizing serum antibodies cross-reacted with Omicron variants as well as more distantly related sarbecoviruses. Because serum neutralizing responses against Omicron strains and other sarbecoviruses were abrogated after pre-clearing with Wuhan-1 spike protein, antibodies induced by XBB.1.5 boosting in humans focus on conserved epitopes targeted by the antecedent mRNA-1273 primary series. Thus, the antibody response to Omicron-based boosters in humans is imprinted by immunizations with historical mRNA-1273 vaccines, but this outcome may be beneficial as it drives expansion of cross-neutralizing antibodies that inhibit infection of emerging SARS-CoV-2 variants and distantly related sarbecoviruses.

Vaccine Effectiveness against GP-Attended Symptomatic COVID-19 and Hybrid Immunity among Adults in Hungary during the 2022-2023 Respiratory Season Dominated by Different SARS-CoV-2 Omicron Subvariants

Hungary provides the opportunity to evaluate the effectiveness of COVID-19 vaccination in a setting where naturally acquired immunity and hybrid immunity are likely to play a greater role due to suboptimal vaccination coverage.

METHODS

A test-negative study was conducted during the 2022-2023 respiratory season at the primary care level to determine the effectiveness of at least one COVID-19 booster dose in preventing medically attended symptomatic RT-PCR-confirmed SARS-CoV-2 infection in adults. Unvaccinated patients were used as a reference group.

RESULTS

A total of 247 cases and 1073 controls were included in the analysis. CVE was 56.8% (95% CI: 11.9-78.8%) in the population aged 60 years and older and 2.3% (95% CI: -50.0-36.3%) in the younger adults against COVID-19 caused by Omicron subvariants, mainly BA.5, BQ.1, and XBB.1. Self-reported COVID-19 in the 60-365 days prior to the current illness did not confer protection against reinfection without vaccination, but together with booster vaccination, it reduced the risk of COVID-19 by 63.0% (95% CI: -28.0-89.3%) and 87.6% (95% CI: 26.4-97.9%) among the 18-59 and 60+ age groups, respectively.

CONCLUSIONS

CVE against COVID-19 was moderately high in the 60+ age groups. Because of the benefit of hybrid immunity, persons with previous SARS-CoV-2 infection should still be considered for vaccination campaigns.

Immunological imprinting shapes the specificity of human antibody responses against SARS-CoV-2 variants

The spike glycoprotein of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) continues to accumulate substitutions, leading to breakthrough infections of vaccinated individuals. It remains unclear if exposures to antigenically distant SARS-CoV-2 variants can overcome memory B cell biases established by initial SARS-CoV-2 encounters. We determined the specificity and functionality of antibody and B cell responses following exposure to BA.5 and XBB variants in individuals who received ancestral SARS-CoV-2 mRNA vaccines. BA.5 exposures elicited antibody responses that targeted epitopes conserved between the BA.5 and ancestral spike. XBB exposures also elicited antibody responses that primarily targeted epitopes conserved between the XBB.1.5 and ancestral spike. However, unlike BA.5, a single XBB exposure elicited low frequencies of XBB.1.5-specific antibodies and B cells in some individuals. Pre-existing cross-reactive B cells and antibodies were correlated with stronger overall responses to XBB but weaker XBB-specific responses, suggesting that baseline immunity influences the activation of variant-specific SARS-CoV-2 responses.

Risk of subsequent SARS-CoV-2 infection among vaccinated employees with or without hybrid immunity acquired early in the Omicron-predominant era of the COVID-19 pandemic

BACKGROUND

Hybrid immunity, from COVID-19 vaccination followed by SARS-CoV-2 infection acquired after its Omicron variant began predominating, has provided greater protection than vaccination alone against subsequent infection over 1-3 months of observation. Its longer-term protection is unknown.

METHODS

We conducted a retrospective cohort study of COVID-19 case incidence among healthcare personnel (HCP) mandated to be vaccinated and report on COVID-19-associated symptoms, high-risk exposures, or known-positive test results to an employee health hotline. We compared cases with hybrid immunity, defined as incident COVID-19 during the first 6 weeks of Omicron-variant predominance (run-in period), to those with immunity from vaccination alone during the run-in period. Time until COVID-19 infection over 13 subsequent months (observation period) was analyzed by standard survival analysis.

RESULTS

Of 5867 employees, 641 (10.9%, 95% confidence interval [CI]: 10.1%-11.8%) acquired hybrid immunity during the run-in period. Of these, 104 (16.2%, 95% CI: 13.5%-19.3%) experienced new SARS-CoV-2 infection during the 13-month observation period, compared to 2177 (41.7%, 95% CI: 40.3%-43.0%) of the 5226 HCP without hybrid immunity. Time until incident infection was shorter among the latter (hazard ratio: 3.09, 95% CI: 2.54-3.78).

CONCLUSIONS

In a cohort of vaccinated employees, Omicron-era acquired SARS-CoV-2 hybrid immunity was associated with significantly lower risk of subsequent infection over more than a year of observation-a time period far longer than previously reported and during which three, progressively more resistant, Omicron subvariants became predominant. These findings can inform institutional policy and planning for future COVID-19 additional vaccine dosing requirements for employees, for surveillance programs, and for risk modification efforts.

A mini review of reinfection with the SARS-CoV-2 Omicron variant

Background

COVID-19 has caused severe morbidity and mortality worldwide. After the end of the dynamic zero-COVID policy in China in December, 2022, concerns regarding reinfection were raised while little was known due to the lack of surveillance data in this country.

Aims

This study reviews the probability, risk factors, and severity of severe acute respiratory syndrome coronavirus 2 Omicron variant reinfection, as well as the interval between infections, risk of onward transmission by reinfected cases, and the role of booster vaccination against reinfection.

Sources

References for this review were identified through searches of PubMed and Web of Science up to September 24, 2023.

Results

The rate of reinfection ranges from 3.1% to 13.0%. Factors associated with a higher risk of reinfection include being female, having comorbidities, and being unvaccinated. Reinfection with the BA.4 or BA.5 variant occurs approximately 180 days after the initial infection. Reinfections are less clinically severe than primary infections, and there is evidence of lower transmissibility. The debate surrounding the effectiveness and feasibility of booster vaccinations in preventing reinfection continues.

Conclusions

The reinfection rate during the Omicron epidemic is significantly higher than in previous epidemic periods. However, the symptoms and infectivity of reinfection were weaker than those of the prior infection. Medical staff and individuals at high risk of reinfection should be vigilant. The efficacy of booster vaccinations in reducing reinfection is currently under debate.

Age-Related Differences in Neutralizing Antibody Responses against SARS-CoV-2 Delta and Omicron Variants in 151 SARS-CoV-2-Naïve Metropolitan Residents Boosted with BNT162b2

BACKGROUND

Although age negatively correlates with vaccine-induced immune responses, whether the vaccine-induced neutralizing effect against variants of concern (VOCs) substantially differs across age remains relatively poorly explored. In addition, the utility of commercial binding assays developed with the wild-type SARS-CoV-2 for predicting the neutralizing effect against VOCs should be revalidated.

METHODS

We analyzed 151 triple-vaccinated SARS-CoV-2-naïve individuals boosted with BNT162b2 (Pfizer-BioNTech). The study population was divided into young adults (age < 30), middle-aged adults (30 ≤ age < 60), and older adults (age ≥ 60). The plaque reduction neutralization test (PRNT) titers against Delta (B.1.617.2) and Omicron (B.1.1.529) variants were compared across age. Antibody titers measured with commercial binding assays were compared with PRNT titers.

RESULTS

Age-related decline in neutralizing titers was observed for both Delta and Omicron variants. Neutralizing titers for Omicron were lower than those against Delta in all ages. The multiple linear regression model demonstrated that duration from third dose to sample collection and vaccine types were also significant factors affecting vaccine-induced immunity along with age. The correlation between commercial binding assays and PRNT was acceptable for all age groups with the Delta variant, but relatively poor for middle-aged and older adults with the Omicron variant due to low titers.

CONCLUSIONS

This study provides insights into the age-related dynamics of vaccine-induced immunity against SARS-CoV-2 VOCs, corroborating the need for age-specific vaccination strategies in the endemic era where new variants continue to evolve. Moreover, commercial binding assays should be used cautiously when estimating neutralizing titers against VOCs, particularly Omicron.

Spatiotemporal dynamics and epidemiological impact of SARS-CoV-2 XBB lineage dissemination in Brazil in 2023

The SARS-CoV-2 XBB is a group of highly immune-evasive lineages of the Omicron variant of concern that emerged by recombining BA.2-descendent lineages and spread worldwide during 2023. In this study, we combine SARS-CoV-2 genomic data (n = 11,065 sequences) with epidemiological data of severe acute respiratory infection (SARI) cases collected in Brazil between October 2022 and July 2023 to reconstruct the space-time dynamics and epidemiologic impact of XBB dissemination in the country. Our analyses revealed that the introduction and local emergence of lineages carrying convergent mutations within the Spike protein, especially F486P, F456L, and L455F, propelled the spread of XBB* lineages in Brazil. The average relative instantaneous reproduction numbers of XBB* + F486P, XBB* + F486P + F456L, and XBB* + F486P + F456L + L455F lineages in Brazil were estimated to be 1.24, 1.33, and 1.48 higher than that of other co-circulating lineages (mainly BQ.1*/BE*), respectively. Despite such a growth advantage, the dissemination of these XBB* lineages had a reduced impact on Brazil's epidemiological scenario concerning previous Omicron subvariants. The peak number of SARI cases from SARS-CoV-2 during the XBB wave was approximately 90%, 80%, and 70% lower than that observed during the previous BA.1*, BA.5*, and BQ.1* waves, respectively. These findings revealed the emergence of multiple XBB lineages with progressively increasing growth advantage, yet with relatively limited epidemiological impact in Brazil throughout 2023. The XBB* + F486P + F456L + L455F lineages stand out for their heightened transmissibility, warranting close monitoring in the months ahead.

IMPORTANCE

Brazil was one the most affected countries by the SARS-CoV-2 pandemic, with more than 700,000 deaths by mid-2023. This study reconstructs the dissemination of the virus in the country in the first half of 2023, a period characterized by the dissemination of descendants of XBB.1, a recombinant of Omicron BA.2 lineages evolved in late 2022. The analysis supports that XBB dissemination was marked by the continuous emergence of indigenous lineages bearing similar mutations in key sites of their Spike protein, a process followed by continuous increments in transmissibility, and without repercussions in the incidence of severe cases. Thus, the results suggest that the epidemiological impact of the spread of a SARS-CoV-2 variant is influenced by an intricate interplay of factors that extend beyond the virus's transmissibility alone. The study also underlines the need for SARS-CoV-2 genomic surveillance that allows the monitoring of its ever-shifting composition.

Previous SARS-CoV-2 infections and their impact on the protection from reinfection during the Omicron BA.5 wave - a nested case-control study among vaccinated adults in Sweden

Objectives

We evaluated the protection afforded by SARS-CoV-2 infection-induced immunity against reinfection among working-age vaccinated individuals during a calendar period from June to December 2022 when Omicron BA.5 was the dominating subvariant in Scania County, Sweden.

Methods

The study cohort (n = 71,592) mainly consisted of health care workers. We analyzed 4144 infected cases during the Omicron BA.5 dominance and 41,440 sex- and age-matched controls with conditional logistic regression.

Results

The average protection against reinfection was marginal (16%, 95% confidence interval [CI] 7-23%) during the study period but substantially higher for recent infections. Recent infection (3-6 months) with Omicron BA.2 and BA.5 offered strong protection (86%, 95% CI 68-94% and 78%, 95% CI 69-84%), whereas more distant infection (6-12 months) with Omicron BA.1, BA.2, and the variants before Omicron offered marginal or no protection.

Conclusions

These findings suggest that infection-induced immunity contributes to short-term population protection against infection with the subvariant BA.5 among working-age vaccinated individuals but wanes considerably with time, independent of the virus variant.

Extensive transmission of SARS-CoV-2 BQ.1* variant in a population with high levels of hybrid immunity: A prevalence survey

OBJECTIVES

The SARS-CoV-2 BQ.1* variant rapidly spread globally in late 2022, posing a challenge due to its increased immune evasion.

METHODS

We conducted a prevalence survey in Brazil from November 16 to December 22, 2022, as part of a cohort study. We conducted interviews and collected nasal samples for reverse transcription-polymerase chain reaction (RT-PCR) testing and whole-genome sequencing. Cumulative incidence was estimated using RT-PCR positivity, cycle threshold values, and external data on the dynamics of RT-PCR positivity following infection.

RESULTS

Among 535 participants, 54% had documented SARS-CoV-2 exposure before this outbreak and 74% had received COVID-19 vaccination. In this study, 14.8% tested positive for SARS-CoV-2, with BQ.1* identified in 90.7% of cases. Using case data and cycle threshold values, cumulative incidence was estimated at 56% (95% confidence interval, 36-88%). Of the 79 positive participants, 48.1% had a symptomatic illness, with a lower proportion fulfilling the World Health Organization COVID-19 case definition compared to prior Omicron waves. No participants required medical attention.

CONCLUSIONS

Despite high population-level hybrid immunity, the BQ.1* variant attacked 56% of our population. Lower disease severity was associated with BQ.1* compared to prior Omicron variants. Hybrid immunity may provide protection against future SARS-CoV-2 variants but in this case was not able to prevent widespread transmission.

Antibody and B Cell Responses to SARS-CoV-2 Infection and Vaccination: The End of the Beginning

As the COVID-19 pandemic has evolved during the past years, interactions between human immune systems, rapidly mutating and selected SARS-CoV-2 viral variants, and effective vaccines have complicated the landscape of individual immunological histories. Here, we review some key findings for antibody and B cell-mediated immunity, including responses to the highly mutated omicron variants; immunological imprinting and other impacts of successive viral antigenic variant exposures on antibody and B cell memory; responses in secondary lymphoid and mucosal tissues and non-neutralizing antibody-mediated immunity; responses in populations vulnerable to severe disease such as those with cancer, immunodeficiencies, and other comorbidities, as well as populations showing apparent resistance to severe disease such as many African populations; and evidence of antibody involvement in postacute sequelae of infection or long COVID. Despite the initial phase of the pandemic ending, human populations will continue to face challenges presented by this unpredictable virus.

Immunological imprinting shapes the specificity of human antibody responses against SARS-CoV-2 variants

The spike glycoprotein of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) continues to accumulate substitutions, leading to breakthrough infections of vaccinated individuals and prompting the development of updated booster vaccines. Here, we determined the specificity and functionality of antibody and B cell responses following exposure to BA.5 and XBB variants in individuals who received ancestral SARS-CoV-2 mRNA vaccines. BA.5 exposures elicited antibody responses that primarily targeted epitopes conserved between the BA.5 and ancestral spike, with poor reactivity to the XBB.1.5 variant. XBB exposures also elicited antibody responses that targeted epitopes conserved between the XBB.1.5 and ancestral spike. However, unlike BA.5, a single XBB exposure elicited low levels of XBB.1.5-specific antibodies and B cells in some individuals. Pre-existing cross-reactive B cells and antibodies were correlated with stronger overall responses to XBB but weaker XBB-specific responses, suggesting that baseline immunity influences the activation of variant-specific SARS-CoV-2 responses.

Effectiveness of primary series, first, and second booster vaccination of monovalent mRNA COVID-19 vaccines against symptomatic SARS-CoV-2 infections and severe diseases during the SARS-CoV-2 omicron BA.5 epidemic in Japan: vaccine effectiveness real-time surveillance for SARS-CoV-2 (VERSUS)

BACKGROUND

This study aimed to evaluate VE of primary, first, and second booster ancestral-strain monovalent mRNA COVID-19 vaccination against symptomatic infections and severe diseases in Japan.

METHODS

We conducted a test-negative case-control study. We included medically attended episodes and hospitalizations involving individuals aged ≥ 16 with signs and symptoms from July to November 2022, when Omicron BA.5 was dominant nationwide. To evaluate VE, we calculated adjusted ORs of vaccination among test-positive versus test-negative individuals using a mixed-effects logistic regression.

RESULTS

For VE against symptomatic infections among individuals aged 16 to 59, VE of primary vaccination at > 180 days was 26.1% (95% CI: 10.6-38.8%); VE of the first booster was 58.5% (48.4-66.7%) at ≤ 90 days, decreasing to 41.1% (29.5-50.8%) at 91 to 180 days. For individuals aged ≥ 60, VE of the first booster was 42.8% (1.7-66.7%) at ≤ 90 days, dropping to 15.4% (-25.9-43.2%) at 91 to 180 days, and then increasing to 44.0% (16.4-62.5%) after the second booster. For VE against severe diseases, VE of the first and second booster was 77.3% (61.2-86.7%) at ≤ 90 days and 55.9% (23.4-74.6%) afterward.

CONCLUSION

mRNA booster vaccination provided moderate protection against symptomatic infections and high-level protection against severe diseases during the BA.5 epidemic in Japan.

Immune response and severity of Omicron BA.5 reinfection among individuals previously infected with different SARS-CoV-2 variants

Introduction

COVID-19 continues to spread worldwide, with an increasing number of individuals experiencing reinfection after recovering from their primary infection. However, the nature and progression of this infection remain poorly understood. We aimed to investigate the immune response, severity and outcomes of Omicron BA.5 reinfection among individuals previously infected with different SARS-CoV-2 variants.

Methods

We enrolled 432 COVID-19 cases who had experienced prior infection with the ancestral SARS-CoV-2 virus, Delta variant or Omicron BA.2 variant between January 2020 and May 2022 in Guangzhou, China. All cases underwent follow-up from March to April, 2023 through telephone questionnaires and clinical visits. Nasal lavage fluid and peripheral blood were collected to assess anti-RBD IgA, anti-RBD IgG and virus-specific IFN-γ secreting T cells.

Results

Our study shows that 73.1%, 56.7% and 12.5% of individuals with a prior infection of the ancestral virus, Delta or Omicron BA.2 variant experienced reinfection with the BA.5 variant, respectively. Fever, cough and sore throat were the most common symptoms of BA.5 reinfection, with most improving within one week and none progressing to a critical condition. Compared with individuals without reinfection, reinfected patients with a prior Delta infection exhibited elevated levels of nasal anti-RBD IgA, serum anti-RBD IgG and IFN-γ secreting T cells, whereas there was no noticeable change in reinfected individuals with a prior BA.2 infection.

Conclusion

These results suggest that BA.5 reinfection is common but severe outcomes are relatively rare. Reinfection with a novel SARS-CoV-2 variant different from the prior infection may induce a more robust immune protection, which should be taken into account during vaccine development.

Protective effect of previous infection and vaccination against reinfection with BA.5 Omicron subvariant: a nationwide population-based study in Japan

Background

The Omicron variant of SARS-CoV-2 was reported to evade immunity derived from vaccination and previous infection. A better understanding of hybrid immunity informs effective infection control strategies. Since the reinfection risk was not well-assessed in East Asia, this study aims to evaluate the risk of infection with Omicron subvariant BA.5 among previously infected individuals in Japan.

Methods

All notified cases were extracted from the Japanese national COVID-19 surveillance database including 20,297,335 records up to 25 September 2022. Reinfection with BA.5 was defined as the infection notified during the BA.5 dominated period with any prior SARS-CoV-2 infection. The protective effect of prior infections against reinfections with BA.5 was estimated by applying a case-population design and the protective effect of vaccination was estimated by a multivariable Cox regression adjusting for age, sex, variants of prior infection, and the time since the last vaccination.

Findings

Among 19,830,548 SARS-CoV-2 first infections, 233,424 (1.2%) were reinfected with BA.5. The protective effect against BA.5 reinfection of prior infection with Wuhan strain was 46%, Alpha variant was 35%, Delta variant was 41%, and BA.1/BA.2 subvariant was 74%. The reduced risk of BA.5 reinfection by 7%, 33%, and 66% was associated with two, three, and four doses of vaccination, respectively, compared with one-dose vaccination.

Interpretation

The prior infections with Omicron subvariant BA.1/BA.2 protected BA.5 reinfection more than pre-Omicron variants. Increased frequency of vaccination led to more protection from reinfection with BA.5. Up-to-date vaccination may be encouraged to prevent future reinfection among the previously infected population.

Funding

None.

Safety and immunogenicity of multivalent SARS-CoV-2 protein vaccines: a randomized phase 3 trial

Background

COVID-19 vaccines that offer broad-spectrum protection are needed. We aimed to evaluate the safety and immunogenicity of multivalent vaccines, SCTV01E and SCTV01C, and compare them with an inactivated vaccine.

Methods

In the phase 3 trial (ClinicalTrials.gov: NCT05323461), adult participants previously vaccinated with Sinopharm's inactivated SARS-CoV-2 vaccine (BBBIP-CorV) were assigned to receive one booster dose of BBBIP-CorV, 20 μg SCTV01C, or 30 μg SCTV01E. The primary endpoint was to evaluate the geometric mean titers (GMT) of neutralizing antibody (nAb) against the Delta and Omicron BA.1 variants on day 28 after injection. Additional endpoints included GMTs of nAb against Delta (B.1.617.2) and Omicron BA.1 variants on day 180, GMTs against BA.5 on day 28, as well as solicited adverse events (AEs) within seven days, unsolicited AEs within 28 days, and serious AEs, AEs of special interest within 180 days after vaccination.

Findings

Between May 30, 2022 and October 28, 2022, a total of 1351 participants were randomized to BBBIP-CorV, SCTV01C, or SCTV01E in a 1:1:1 ratio, with immunogenicity assessments performed on the first 300 participants. For BBBIP-CorV, SCTV01C, and SCTV01E groups, the day 28 GMTs of neutralizing antibody against Omicron BA.1 were a 2.38-, 19.37-, and 28.06-fold increase from baseline; the GMTs against Omicron BA.5 were 2.07-, 15.89- and 21.11-fold increases; the GMTs against Delta variants were 1.97-, 12.76-, and 15.88-fold increases, respectively. The day 28 geometric mean ratio (GMR) of SCTV01C/BBIBP-CorV for Omicron BA.1 was 6.49 (95% CI: 4.75, 8.88), while the GMR of SCTV01E/BBIBP-CorV was 9.56 (95% CI: 6.85, 13.33). For the Delta variant, the day 28 GMR of SCTV01C/BBIBP-CorV was 6.26 (95% CI: 4.78, 8.19), and the day 28 GMR of SCTV01E/BBIBP-CorV was 7.26 (95% CI: 5.51, 9.56). On Day 180, the GMTs against Omicron BA.1 were 2.80-, 9.51-, and 15.56-fold increase from baseline, while those against Delta were 1.58-, 5.49-, and 6.63-fold for BBBIP-CorV, SCTV01C, and SCTV01E groups, respectively. Subgroup analyses showed that SCTV01C and SCTV01E induced uniformly high GMTs against both BA.1 and BA.5, demonstrating its superiority over BBIBP-CorV, regardless of baseline GMT levels. Safety and reactogenicity were similar among the three vaccines. Most AEs were Grade 1 or 2. There were 15 ≥Grade 3 AEs: 6 in the BBIBP-CorV group, 4 in the SCTV01C group and 5 in the SCTV01E group. No SAE was reported and one grade 1 AESI (Bell's palsy) was observed in SCTV01C group.

Interpretation

A booster dose of the tetravalent vaccine SCTV01E consistently induced high neutralizing antibody responses against Omicron BA.1, BA.5, and Delta variants, demonstrating superiority over inactivated vaccine. There is evidence to suggest that SCTV01E may have GMT superiority over bivalent vaccine SCTV01C against Delta, BA.1 and BA.5 variants.

Funding

This study was sponsored by Sinocelltech Ltd., and funded by the Beijing Science and Technology Planning Project [Z221100007922012] and the National Key Research and Development Program of China [2022YFC0870600].

Catch-up antibody responses and hybrid immunity in mRNA vaccinated patients at risk of severe COVID-19

BACKGROUND

The immunogenicity of repeated vaccination and hybrid immunity in vulnerable patients remains unclear.

METHODS

We studied the impact of iterative Covid-19 mRNA vaccination and hybrid immunity on antibody levels in immunosuppressed subjects. Patients with liver cirrhosis (n = 38), survivors of allogeneic haematopoietic stem cell transplantation (allo-HSCT) (n = 36) and patients with autoimmune liver disease (n = 14) along with healthy controls (n = 20) were monitored for SARS-CoV-2-S1 IgG after their 1st-3rd vaccine doses, 31 of whom became infected with the Omicron variant after the 2nd dose. Ten uninfected allo-HSCT recipients received an additional 4th vaccine dose.

RESULTS

Unexpectedly, immunosuppressed patients achieved antibody levels in parity with controls after the 3rd vaccine dose. In all study cohorts, hybrid immunity (effect of vaccination and natural infection) resulted in approximately 10-fold higher antibody levels than vaccine-induced immunity alone.

CONCLUSIONS

Three doses of the Covid-19 mRNA vaccine entailed high antibody concentrations even in immunocompromised individuals, and hybrid-immunity resulted further augmented levels than vaccination alone. Clinical trial registration: EudraCT 2021-000349-42.

Bivalent Vaccine Effectiveness Among Adults Aged ≥65 Years During the BA.5-Predominant Period in Japan: The VENUS Study

Background

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Omicron BA.5 became prevalent in July 2022 in Japan. Bivalent messenger RNA (mRNA) vaccines were approved as booster doses for individuals who received the primary series or booster dose by monovalent vaccines. We aimed to assess the effectiveness of bivalent vaccines in Japanese adults aged ≥65 years.

Methods

We conducted a population-based cohort study using data collected from January 2019 to February 2023 in Japan. We included individuals aged ≥65 years in a municipality who received the first or second booster dose of monovalent mRNA vaccines. We estimated the effectiveness of the second or third booster dose of bivalent mRNA vaccines during the Omicron BA.5-predominant period (July-December 2022), compared with ≥90 days after the booster dose of monovalent vaccines. We used a Cox proportional hazard regression model with vaccination status as a time-dependent covariate.

Results

A total of 81 977 individuals aged ≥65 years (mean [standard deviation] age, 78.3 [7.4] years; 33 487 male [40.8%]) were included in the study cohort. Among them, 57 396 were vaccinated with the second or third dose of bivalent vaccines (BA.1 or BA.4/5). The effectiveness against coronavirus disease 2019 (COVID-19) was estimated to be 57.9% (95% confidence interval, 52.7%-62.5%) for ≥14 days after the second or third bivalent booster dose, compared with 90 days after the first or second monovalent booster dose.

Conclusions

The study showed that the bivalent mRNA vaccines as the second and third doses would provide protection against COVID-19 among adults ≥65 years in Japan.

Factors associated with COVID-19 vaccination coverage in hypertensive patients with Omicron infection in Shanghai, China

The potential future burden of COVID-19 is determined by the level of susceptibility of the population to infection. The protective effect provided by those previously infected diminishes over several months, while individuals with mixed immunity have the highest degree and persistence of protection. This study aimed to clarify the vaccination status of COVID-19 patients with hypertension and to analyze the characteristics and risk factors of non-vaccinated patients to protect this vulnerable population in the future. The study ultimately enrolled 4576 hypertensive patients with Omicron infection from April 6, 2022, to May 15, 2022. Among them, 3556 patients (77.7%) had received at least one dose of vaccine, and 2058 patients (45.0%) received a booster dose. In the multivariate logistic analysis, male (OR 1.328, 95% CI 1.138-1.550, p < .001), age (60-69 years vs.18-49 years) (OR 0.348, 95% CI 0.270-0.448, p < .001), age (≥70 years vs.18-49 years) (OR 0.130, 95% CI 0.100-0.169, p < .001), diabetes mellitus (OR 0.553, 95% CI 0.463-0.661, p < .001), chronic pulmonary diseases (OR 0.474, 95% CI 0.260-0.863, p = .015), chronic kidney disease (OR 0.177, 95% CI 0.076-0.410, p < .001), and cancer (OR 0.225, 95% CI 0.094-0.535, p = .001) were associated with vaccinated status. The vaccine coverage rate, especially the booster vaccine, was low for hypertensive patients with Omicron infection. Females, increasing age, and coexisting chronic diseases were associated with more inadequate vaccine coverage in hypertensive COVID-19 patients. Targeted interventions are required to address the under-vaccination of diverse hypertensive populations.

The effects of amino acid substitution of spike protein and genomic recombination on the evolution of SARS-CoV-2

Over three years' pandemic of 2019 novel coronavirus disease (COVID-19), multiple variants and novel subvariants have emerged successively, outcompeted earlier variants and become predominant. The sequential emergence of variants reflects the evolutionary process of mutation-selection-adaption of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Amino acid substitution/insertion/deletion in the spike protein causes altered viral antigenicity, transmissibility, and pathogenicity of SARS-CoV-2. Early in the pandemic, D614G mutation conferred virus with advantages over previous variants and increased transmissibility, and it also laid a conservative background for subsequent substantial mutations. The role of genomic recombination in the evolution of SARS-CoV-2 raised increasing concern with the occurrence of novel recombinants such as Deltacron, XBB.1.5, XBB.1.9.1, and XBB.1.16 in the late phase of pandemic. Co-circulation of different variants and co-infection in immunocompromised patients accelerate the emergence of recombinants. Surveillance for SARS-CoV-2 genomic variations, particularly spike protein mutation and recombination, is essential to identify ongoing changes in the viral genome and antigenic epitopes and thus leads to the development of new vaccine strategies and interventions.

BNT162b2 vaccine protection against omicron and effect of previous infection variant and vaccination sequence among children and adolescents in Singapore: a population-based cohort study

BACKGROUND

Information on variant-specific vaccine protection and the effect of previous infection variant is scarce in children. We aimed to ascertain the level of protection conferred by BNT162b2 COVID-19 vaccination against omicron variant infection (BA.4 or BA.5, and XBB) in a previously infected national paediatric cohort. We also explored the association between sequence of previous infection (variant) and vaccination on protection.

METHODS

We did a retrospective, population-based cohort study using the national databases of all confirmed SARS-CoV-2 infections, vaccines administered, and demographic records maintained by the Ministry of Health, Singapore. The study cohort consisted of children aged 5-11 years and adolescents aged 12-17 years who had a previous SARS-CoV-2 infection from Jan 1, 2020, to Dec 15, 2022. People who were infected during the pre-delta period or were immunocompromised (received three vaccination doses [children 5-11 years old] and four vaccinations doses [adolescents 12-17 years old]) were excluded. Those who had multiple episodes of infection before the study start date, were not vaccinated before infection but completed three doses, received bivalent mRNA vaccine, or received non-mRNA vaccine doses were also excluded. All SARS-CoV-2 infections confirmed by reverse transcriptase polymerase chain reaction or rapid antigen testing were grouped into delta, BA.1, BA.2, BA.4 or BA.5, or XBB variants using a combination of whole-genome sequencing, S-gene target failure results, and imputation. For BA.4 or BA.5, the study outcome period was June 1-Sept 30, 2022, and for XBB variants the outcome period was Oct 18-Dec 15, 2022. Incidence rate ratios between vaccinated and unvaccinated were derived using adjusted Poisson regressions and vaccine effectiveness was estimated as (1-risk ratio) × 100%.

FINDINGS

135 197 people aged 5-17 years (79 332 children and 55 865 adolescents) were included in the cohort for the vaccine effectiveness analysis against omicron BA.4 or BA.5, and 164 704 people aged 5-17 years (97 235 children and 67 469 adolescents) were included for the analysis against omicron XBB. Approximately 47% of participants were female and 53% were male. Among those previously infected, vaccine effectiveness against BA.4 or BA.5 infection in fully vaccinated children (two doses) was 74·0% (95% CI 67·7-79·1) and in adolescents (three doses) was 85·7% (80·2-89·6). Against XBB, protection conferred with full vaccination was lower at 62·8% (95% CI 42·3-76·0) in children and 47·9% (20·2-66·1) in adolescents. In children, receipt of two-dose vaccination before first SARS-CoV-2 infection provided them with the highest protection against subsequent BA.4 or BA.5 infection at 85·3% (95% CI 80·2-89·1); however, this was not shown to be the case for adolescents. First infection variant had an effect on vaccine effectiveness against omicron BA.4 or BA.5 reinfection in the following descending order: BA.2 conferred the highest protection (92·3% [95% CI 88·9-94·7] in children and 96·4% [93·5-98·0] in adolescents) followed by BA.1 (81·9% [75·9-86·4] in children and 95·0% [91·6-97·0] in adolescents), and delta which conferred the lowest protection (51·9% [5·3-75·6] in children and 77·5% [63·9-86·0] in adolescents).

INTERPRETATION

In previously infected children and adolescents, BNT162b2 vaccination provided additional protection against omicron BA.4 or BA.5 and XBB variants compared with those who remained unvaccinated. Hybrid immunity against XBB was lower than against BA.4 or BA.5, especially in adolescents. Early vaccination of previously uninfected children before their first SARS-CoV-2 exposure could potentially strengthen population immunity resilience against future variants.

FUNDING

None.

The Omicron Variant Reinfection Risk among Individuals with a Previous SARS-CoV-2 Infection within One Year in Shanghai, China: A Cross-Sectional Study

Reinfection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants due to immune escape is challenging for the global response to the pandemic. We estimated the Omicron reinfection prevalence among people who had a previous SARS-CoV-2 infection in Shanghai, China. We conducted a telephone survey in December 2022 with those who had previously been infected with Omicron between March and May 2022. Information on their demographics, coronavirus disease 2019 (COVID-19) testing, and vaccination history was collected. The overall and subgroup reinfection rates were estimated and compared. Among the 1981 respondents who were infected between March and May 2022, 260 had positive nucleic acid or rapid antigen tests in December 2022, with an estimated reinfection rate of 13.1% (95% confidence interval [95% CI]: 11.6-14.6). The reinfection rate for those who had a booster vaccination was 11.4% (95% CI: 9.2-13.7), which was significantly lower than that for those with an incomplete vaccination series (15.2%, 95% CI: 12.3-18.1) (adjusted odds ratio [aOR]: 0.579; 95% CI: 0.412-0.813). Reinfection with the Omicron variant was lower among individuals with a previous SARS-CoV-2 infection and those who had a booster vaccination, suggesting that hybrid immunity may offer protection against reinfection with Omicron sublineages.