Longitudinal observation and decline of neutralizing antibody responses in the three months following SARS-CoV-2 infection in humans

Waning of anti-SARS-CoV-2 antibodies after the first wave of the COVID-19 pandemic in 2020: A 12-month-evaluation in three population-based European studies

OBJECTIVES

We described waning in anti-SARS-CoV-2 IgG in adult general populations infected during the first wave of the COVID-19 pandemic in 2020 across three European countries.

METHODS

Coordinated analyses were conducted separately in three population-based cohorts with complementary follow-up schedules: the KoCo19 (Germany), EpiCov (France), and CON-VINCE (Luxembourg) cohorts. Serological follow-up was based on the anti-SARS-CoV-2 ELISA-S IgG (Euroimmun) assay. We selected all adults aged 18-79 who had a positive serology (IgG optical density (OD) ratio ≥1.1) between February and July 2020, and at least one subsequent IgG measurement within the following 12 months, while still non-vaccinated.

RESULTS

The proportion of seroreversion was 0% within the four first months, based on Koco19 data (n = 65 participants). In the longer term, 31.3% of participants had seroreverted at 6 months (95%CI: 24.4-39.1) (based on EpiCov data, n = 599), 31.3% (95%CI: 11.0-58.7) at 12 months (based on CON-VINCE data, n = 16). From EpiCov data, both baseline low IgG levels and seroneutralization negativity remained predictive of seroreversion in multivariable analysis.

CONCLUSION

From population-based cohorts, anti-S IgG levels remained stable during the first 4 months following SARS-CoV-2 infection. Most of the decay occurred afterward; nearly one-third of people seroreverted 6 and 12 months later. Low IgG levels and seroneutralization negativity were independent predictors of seroreversion.

The comprehensive insights into the B-cells-mediated immune response against COVID-19 infection amid the ongoing evolution of SARS-CoV-2

The antibody-mediated immune response is crucial for the development of protective immunity against SARS-CoV-2, the virus responsible for the COVID-19 pandemic. Understanding the interaction between SARS-CoV-2 and the immune system is critical because new variants emerge as a result of the virus's ongoing evolution. Understanding the function of B cells in the SARS-CoV-2 infection process is critical for developing effective and long-lasting vaccines against this virus. Triggered by the innate immune response, B cells transform into memory B cells (MBCs). It is fascinating to observe how MBCs provide enduring immune defence, not only eradicating the infection but also safeguarding against future reinfection. If there is a lack of B cell activation or if the B cells are not functioning properly, it can lead to a serious manifestation of the disease and make immunisation less effective. Individuals with disruptions in the B cells have shown increased production of cytokines and chemokines, resulting in a poor prognosis for the disease. Therefore, we have developed an updated review article to gain insight into the involvement of B cells in SARS-CoV-2 infection. The discussion has covered the generation, functioning, and dynamics of neutralising antibodies (nAbs). Furthermore, we have emphasised immunotherapeutics that rely on nAbs.

Persistence and decay of neutralizing antibody responses elicited by SARS-CoV-2 infection and hybrid immunity in a Canadian cohort

A major challenge with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative agent of coronavirus disease 2019 (COVID-19), has been assessing the intensity, dynamics, and determinants of the antibody responses after infection and/or vaccination. Therefore, we aimed to characterize the longitudinal dynamics of the antibody responses among naturally infected individuals and individuals who achieved hybrid immunity in a large Canadian cohort. We demonstrate that anti-Spike IgGs and neutralizing antibody dynamics vary greatly among individuals with COVID-19, in peak antibody levels, rate of waning, and longevity of the antibody response. Additionally, we found an association between robust antibody responses and individuals with severe COVID-19 clinical symptoms during the first-month post-symptom onset. For individuals who achieved hybrid immunity, a robust increase in anti-S1 IgGs and neutralizing antibodies followed the first vaccination dose; however, there was a minimal increase in the anti-S1 IgGs and neutralizing antibody titers after administration of the second dose of the vaccine. Furthermore, neutralizing antibodies elicited by the wild-type virus alone were largely ineffective against emerging variants of concern in our natural infection-only cohort, in contrast to a much broader and more robust neutralization profile observed in individuals who achieved hybrid immunity. Our findings emphasize the need for global SARS-CoV-2 vaccination efforts to further sustain protective immune responses required to minimize viral spread and disease severity in the population. As SARS-CoV-2 variants continue to emerge, understanding the interplay between previous infections, vaccine durability, and virus evolution will be critical for guiding ongoing vaccination strategies.

IMPORTANCE

A major challenge with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative agent of coronavirus disease 2019 (COVID-19), has been assessing the intensity, dynamics, and determinants of the antibody response after infection and/or vaccination. Our paper addresses this in a large Canadian cohort with antibody responses that were generated by natural infection as well as vaccine in some persons studied.

Tracking the evolution of serum antibody levels and influencing factors post-SARS-CoV-2 infection among community residents in Fuzhou City

Objective

To track the level of serum antibodies in Fuzhou residents and analyze the possible influencing factors of serum antibodies, so as to provide a scientific basis for the adjustment of population immunity and prevention and control strategies.

Methods

Residents in the Fuzhou community who had symptoms of covid-19 infection or who had tested positive for nucleic acid or antigen since December 2022 were selected for the questionnaire survey and their sera were collected to analyze the trend of antibody changes, the antibody level was divided into high antibody group and low antibody group according to the literature data. The possible influencing factors of serum antibody level was analyzed by multivariate logistic regression model.

Results

A total of 2,521 Fuzhou residents were adopted in the study, including 223 in the high antibody group and 194 in the low antibody group. A univariate analysis showed that, there were significant differences in age (Z=-4.028, P<0.00), occupation (χ2 = 18.591, P=0.005), typical symptoms after the first infection (χ2 = 9.784, P=0.002), history of surgery (χ2 = 29.542, P<0.001), symptoms lasting more than 2 weeks after the first infection (χ2 = 4.887, P=0.027), smoking (χ2 = 18.524, P<0.001) and drinking (χ2 = 19.578, P<0.001) between the high antibody group and the low antibody group. Multivariate regression models show that, age (OR= 1.011, 95%CI: 1.002~1.020, P=0.017), history of surgery (OR=4.956,95%CI: 2.606~9.423, P<0.001),smoking (OR=2.089, 95%CI: 1.002~4.355, P=0.049), drinking (OR=2.214, 95%CI: 1.066~4.600, P=0.033) were the risk factors affecting antibody level. Typical symptoms after the first infection (OR=0.224, 95%CI: 0.086~0.579, P=0.002) and symptoms lasting more than 2 weeks after the first infection (OR=0.432, 95%CI: 0.258~0.723, P=0.001) were protective factors. By observing the trend of antibody changes in 3, 6 and 9 months, we found that the level of IgG antibody showed a decreasing trend.

Conclusions

The high level of protection was more likely to occur in young adults, people without operation history, people without smoking history, people without drinking history, people with typical symptoms after the first infection and symptoms lasting more than 2 weeks after the first infection. The level of IgG antibody was decreased in general, so it is necessary to strengthen immunization.

Flow cytometric analysis of the SARS coronavirus 2 antibodies in human plasma

COVID-19 is an infectious disease caused by the severe acute respiratory syndrome coronavirus (SARS-CoV-2). Anti-SARS-CoV-2 antibodies can provide information on patient immunity, identify asymptomatic patients, and track the spread of COVID-19. Efforts have been made to develop methods to detect anti-SARS-CoV-2 antibodies in humans. Here, we describe a flow cytometric assay for the simultaneous detection of anti-SARS-CoV-2 IgG and IgM in human plasma. To assess the antibody response against the different SARS-CoV-2 structural proteins, five viral recombinant proteins, including spike protein subunit 1 (S1), N-terminal domain of S1 (S1A), spike receptor-binding domain (RBD), spike protein subunit 2 (S2), and nucleocapsid protein (N), were generated. A comparison of the antibody profiles detected by the assay with plasma from 100 healthy blood donors collected prior to the COVID-19 pandemic and plasma from 100 virologically confirmed COVID-19 patients demonstrated a clear discrimination between the two groups. Among the COVID-19 patients, the antibody responses for the viral proteins, as determined by their prevalence, were anti-RBD IgG = anti-N IgG > anti-S1 IgG > anti-S1A IgG > anti-S2 IgG, and anti-RBD IgM > anti-S1 IgM > anti-N IgM > anti-S2 IgM. The prevalence of anti-SARS-CoV-2 IgG and IgM was not associated with sex, age, race, days after the onset of symptoms, or severity of illness, except for a higher prevalence of anti-S2 IgG being observed in men than in women. The levels of anti-RBD IgG were higher in patients 65 years and older and in patients who had severe symptoms. Similarly, patients who had severe symptoms exhibited higher levels of anti-S1 and anti-S1A IgG than patients who had mild or moderate symptoms. The levels of anti-RBD IgM tended to be higher in men but did not differ among age, race, days after the onset of symptoms, or severity of illness. Our study indicates that the flow cytometric assay, especially using RBD as target antigen, can be used to detect simultaneously anti-SARS-CoV-2 IgG and IgM antibodies in human plasma.

Immunogenicity and safety study of a single dose of SpikoGen® vaccine as a heterologous or homologous intramuscular booster following a primary course of mRNA, adenoviral vector or recombinant protein COVID-19 vaccine in ambulatory adults

BACKGROUND

SpikoGen® is a subunit recombinant Wuhan spike protein produced in insect cells and formulated with Advax-CpG55.2™ adjuvant. It is approved for adult and pediatric use in the Middle East. This study tested the safety and immunogenicity of SpikoGen® as a 3rd, 4th or 5th dose booster following a primary immunisation course of mRNA, adenovirus or SpikoGen® vaccine.

METHODS

The trial recruited participants who had received a previous doses of COVID-19 vaccine more than 3 months prior. Each received a single intramuscular booster dose of SpikoGen® vaccine. Spike and nuclear protein antibody levels were measured at 1 and 3 months post-booster, together with collection of data on SARS-CoV-2 breakthrough infections and symptoms of long COVID.

RESULTS

One-month post-booster, anti-spike IgG, sVNT, and pVNT levels were increased in all groups and there was ∼4-fold neutralizing antibodies against the heterologous Omicron BA.2 and BA.4/5 strains. The SpikoGen®-prime group had the highest levels of anti-spike IgG3, consistent with the Advax-CpG adjuvant driving IgG3 induction. There was no effect of age on the vaccine response. The booster dose was well tolerated with no vaccine-associated serious adverse events. Nine participants (9/74, 12.2 %) had a breakthrough SARS-CoV-2 infection between 2 weeks and 3 months post-booster. No long COVID was observed after breakthrough infections. Breakthrough infection was negatively correlated with baseline anti-nuclear protein IgG seropositivity.

CONCLUSION

A single SpikoGen® booster was well tolerated and stimulated cross- antibody responses against Omicron variants, regardless of the primary vaccine course received. With SARS-CoV-2 variants continuing to evolve, ongoing research is needed into optimum booster strategies.

CLINICALTRIALS

gov registration. NCT05542862.

Multi-antigen serology and a diagnostic algorithm for the detection of arbovirus infections as novel tools for arbovirus preparedness in southeast Europe (MERMAIDS-ARBO): a prospective observational study

BACKGROUND

Arboviruses are increasingly affecting Europe, partly due to the effects of climate change. This increase in range and impact emphasises the need to improve preparedness for emerging arboviral infections that often co-circulate and might have overlapping clinical syndromes. We aimed to strengthen surveillance networks for four clinically relevant arboviruses in southeast Europe.

METHODS

This study reports an in-depth analysis of the MERMAIDS-ARBO prospective observational study in adults (ie, aged ≥18 years) hospitalised with an arbovirus-compatible disease syndrome in 21 hospitals in seven countries in southeast Europe over four arbovirus seasons (May 1-Oct 31, 2016-19) to obtain arbovirus prevalence outcomes. The main objectives of the MERMAIDS-ARBO study, describing the clinical management and outcomes of four arboviruses endemic to southeast Europe, including Crimean-Congo haemorrhagic fever virus (CCHFV), tick-borne encephalitis virus (TBEV), Toscana virus, and West Nile virus (WNV), are reported elsewhere. In this analysis, given the challenges associated with arbovirus diagnostics, we developed a diagnostic algorithm accounting for serology outcomes and sample timing to study arbovirus prevalence in southeast Europe. Serum samples were collected on days 0, 7, 28, and 60 after hospital admission and tested for anti-CCHFV IgG and IgM antibodies with ELISAs (confirmed with an indirect immunofluorescence test) and for IgG and IgM antibodies specific to TBEV, Toscana virus, and WNV with custom-printed protein microarrays (confirmed with virus neutralisation tests). All acute-phase samples were tested by PCR for all four viruses. Descriptive analyses were performed for virus-reactive cases by geography and year, and possible factors (eg, age, sex, and insect bites) associated with virus reactivity were assessed.

FINDINGS

Of 2896 individuals screened, 913 were eligible for inclusion, of whom 863 (514 men, 332 women, and 17 unknown) had samples sent to the study reference laboratories and were included in molecular and serological analyses. Some individuals had insufficient clinical data to be included in the clinical analysis, but met the eligibility criteria for and were included here. Serum sampling was incomplete (eg, samples missing from one or more timepoints or no data on time since symptom onset) for 602 (70%) patients, and the timing of collection was often heterogeneous after symptom onset up to 40 days (average median delay of 5-6 days across all timepoints), affecting the ability to diagnose arbovirus infection by serology. By use of an interpretation table incorporating timing and completeness of sampling, one (<1%) participant had a confirmed recent infection with CCHFV, ten (1%) with TBEV, 40 (5%) with Toscana virus, and 52 (6%) with WNV. Most acute confirmed infections of Toscana virus were found in Albania (25 [63%] of 40), whereas WNV was primarily identified in Romania (36 [69%] of 52). Albania also had the highest overall Toscana virus seropositivity (168 [60%] of 282), mainly explained by patients confirmed to be exposed or previously exposed (104 [62%] of 168). Patients without antibodies to WNV or Toscana virus were significantly younger than patients with antibodies (mean difference -8·48 years [95% CI -12·31 to -4·64] for WNV, and -6·97 years [-9·59 to -4·35] for Toscana virus). We found higher odds of Toscana virus reactivity in men (odds ratio 1·56 [95% CI 1·15 to 2·11]; p=0·0055), WNV reactivity with mosquito bites versus no mosquito bites (2·47 [1·54 to 3·97]; p=0·0002), and TBEV reactivity with tick bites versus no tick bites (2·21 [1·19 to 4·11]; p=0·018).

INTERPRETATION

This study shows that despite incomplete and heterogeneous data, differential diagnosis of suspected arbovirus infections is possible, and the diagnostic interpretation algorithm we propose could potentially be used to strengthen routine diagnostics in clinical settings in areas at risk for arboviral diseases. Our data highlight potential hotspots for arbovirus surveillance and risk factors associated with these particular arbovirus infections.

FUNDING

European Commission and Versatile Emerging infectious disease Observatory.

TRANSLATIONS

For the Greek, Albanian, Romanian, Bosnian, Serbian, and Croatian translation of the summary see Supplementary Materials section.

SARS-CoV-2 serologic surveillance among people living with HIV in Nigeria, April 2022 to January 2023

OBJECTIVES

Evidence indicates that people living with HIV (PLHIV) are more impacted by COVID-19. The burden of SARS-CoV-2 infection among PLHIV is unknown in Nigeria.

METHODS

We conducted repeated cross-sectional SARS-CoV-2 serosurveys in 14 states and the Federal Capital Territory in Nigeria among PLHIV who had an HIV viral load (VL) test during April 2022 to January 2023. Evidence of SARS-CoV-2 immunoglobulin G (IgG) antibodies was assessed using a multiplex bead assay to measure IgG to spike (S), receptor binding domain (RBD), and nucleocapsid (N) proteins to identify potential infection and/or vaccination status.

RESULTS

Between April 2022 and January 2023, 47,614 remnant VL samples were included and tested for SARS-CoV-2 antibodies. Seroprevalence of SARS-CoV-2 infection, defined as IgG antibodies to spike and RBD591 [S+] and nucleocapsid [N+], (S+N+), ranged between 21.1% (95% confidence intervals [CI]: 11.4-31.8) in Ekiti State in January 2023 to 71.4% (95% CI 71.9-81.9) in Gombe State in November 2022, with overall steady trends within and between states over time, across age and sex.

CONCLUSION

High rates of SARS-CoV-2 antibody seroprevalence among PLHIV in Nigeria were observed. This underscores the need to understand the association between HIV and SARS-CoV-2 to inform strategies to reduce the threat posed by COVID-19.

Theoretical and practical considerations for validating antigen-specific B cell ImmunoSpot assays

Owing to their ability to reliably detect even very rare antigen-specific B cells in cellular isolates such as peripheral blood mononuclear cells (PBMC), and doing so robustly in a high throughput-compatible manner, B cell ELISPOT/FluoroSpot (collectively "B cell ImmunoSpot") tests have become increasingly attractive for immune monitoring in regulated settings. Presently, there are no guidelines for the qualification and validation of B cell ImmunoSpot assay results. Here, we propose such guidelines, building on the experience acquired from T cell ImmunoSpot testing in an environment adhering to the requirements of regulatory bodies yet taking the unique features of B cell assays into account. A streamlined protocol is proposed that permits the performance of all tests needed for the formal validation of an antigen-specific B cell ImmunoSpot assay in only three experiments, utilizing 2.2 × 107 PBMC per donor. Subsequently, utilizing only 1-2 × 106 PBMC per sample (obtainable from 1 to 2 mL of blood), a validated multiplexed assay enables accurate quantification of the frequency of antigen-specific memory B cell-derived blasts secreting IgM, IgG, IgA or IgE antibodies. Collectively, such multiplexed B cell ImmunoSpot assays offer immense value for B cell immune monitoring programs due to their ease of implementation, scalability, applicability to essentially any antigenic system, economy of PBMC utilization, and last but not least, the high content information gained.

Distinct CD8+ T-cell types Associated with COVID-19 Severity in Unvaccinated HLA-A2+ Patients

Although emerging data have revealed the critical role of memory CD8+ T cells in preventing and controlling SARS-CoV-2 infection, virus-specific CD8+ T-cell responses against SARS-CoV-2 and its memory and innate-like subsets in unvaccinated COVID-19 patients with various disease manifestations in an HLA-restricted fashion remain to be understood. Here, we show the strong association of protective cellular immunity with mild COVID-19 and unique cell types against SARS-CoV-2 virus in an HLA-A2 restricted manner. ELISpot assays reveal that SARS-CoV-2-specific CD8+ T-cell responses in mild COVID-19 patients are significantly higher than in severe patients, whereas neutralizing antibody responses against SARS-CoV-2 virus significantly correlate with disease severity. Single-cell analyses of HLA-A2-restricted CD8+ T cells, which recognize highly conserved immunodominant SARS-CoV-2-specific epitopes, demonstrate divergent profiles in unvaccinated patients with mild versus severe disease. CD8+ T-cell types including cytotoxic KLRB1 + CD8αα cells with innate-like T-cell signatures, IFNG hi ID3 hi memory cells and IL7R + proliferative stem cell-like memory cells are preferentially observed in mild COVID-19, whereas distinct terminally-differentiated T-cell subsets are predominantly detected in severe COVID-19: highly activated FASL hi T-cell subsets and early-terminated or dysfunctional IL4R + GATA3 + stem cell-like memory T-cell subset. In conclusion, our findings suggest that unique and contrasting SARS-CoV-2-specific CD8+ T-cell profiles may dictate COVID-19 severity.

Multidisciplinary Center Care for Long COVID Syndrome-A Retrospective Cohort Study

BACKGROUND

Persistent multi-organ symptoms after coronavirus disease 2019 (COVID-19) have been termed "long COVID" or "post-acute sequelae of SARS-CoV-2 infection." The complexity of these clinical manifestations posed challenges early in the pandemic as different ambulatory models formed out of necessity to manage the influx of patients. Little is known about the characteristics and outcomes of patients seeking care at multidisciplinary post-COVID centers.

METHODS

We performed a retrospective cohort study of patients evaluated at our multidisciplinary comprehensive COVID-19 center in Chicago, Ill, between May 2020 and February 2022. We analyzed specialty clinic utilization and clinical test results according to severity of acute COVID-19.

RESULTS

We evaluated 1802 patients a median of 8 months from acute COVID-19 onset, including 350 post-hospitalization and 1452 non-hospitalized patients. Patients were seen in 2361 initial visits in 12 specialty clinics, with 1151 (48.8%) in neurology, 591 (25%) in pulmonology, and 284 (12%) in cardiology. Among the patients tested, 742/916 (81%) reported decreased quality of life, 284/553 (51%) had cognitive impairment, 195/434 (44.9%) had alteration of lung function, 249/299 (83.3%) had abnormal computed tomography chest scans, and 14/116 (12.1%) had elevated heart rate on rhythm monitoring. Frequency of cognitive impairment and pulmonary dysfunction was associated with severity of acute COVID-19. Non-hospitalized patients with positive SARS-CoV-2 testing had findings similar to those with negative or no test results.

CONCLUSIONS

The experience at our multidisciplinary comprehensive COVID-19 center shows common utilization of multiple specialists by long COVID patients, who harbor frequent neurologic, pulmonary, and cardiologic abnormalities. Differences in post-hospitalization and non-hospitalized groups suggest distinct pathogenic mechanisms of long COVID in these populations.

Antibodies to the RBD of SARS-CoV-2 spike mediate productive infection of primary human macrophages

The role of myeloid cells in the pathogenesis of SARS-CoV-2 is well established, in particular as drivers of cytokine production and systemic inflammation characteristic of severe COVID-19. However, the potential for myeloid cells to act as bona fide targets of productive SARS-CoV-2 infection, and the specifics of entry, remain unclear. Using a panel of anti-SARS-CoV-2 monoclonal antibodies (mAbs) we performed a detailed assessment of antibody-mediated infection of monocytes/macrophages. mAbs with the most consistent potential to mediate infection were those targeting a conserved region of the receptor binding domain (RBD; group 1/class 4). Infection was closely related to the neutralising concentration of the mAbs, with peak infection occurring below the IC50, while pre-treating cells with remdesivir or FcγRI-blocking antibodies inhibited infection. Studies performed in primary macrophages demonstrated high-level and productive infection, with infected macrophages appearing multinucleated and syncytial. Infection was not seen in the absence of antibody with the same quantity of virus. Addition of ruxolitinib significantly increased infection, indicating restraint of infection through innate immune mechanisms rather than entry. High-level production of pro-inflammatory cytokines directly correlated with macrophage infection levels. We hypothesise that infection via antibody-FcR interactions could contribute to pathogenesis in primary infection, systemic virus spread or persistent infection.

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.

Induction of Fc-dependent functional antibodies against different variants of SARS-CoV-2 varies by vaccine type and prior infection

BACKGROUND

SARS-CoV-2 transmission and COVID-19 disease severity is influenced by immunity from natural infection and/or vaccination. Population-level immunity is complicated by the emergence of viral variants. Antibody Fc-dependent effector functions are as important mediators in immunity. However, their induction in populations with diverse infection and/or vaccination histories and against variants remains poorly defined.

METHODS

We evaluated Fc-dependent functional antibodies following vaccination with two widely used vaccines, AstraZeneca (AZ) and Sinovac (SV), including antibody binding of Fcγ-receptors and complement-fixation in vaccinated Brazilian adults (n = 222), some of who were previously infected with SARS-CoV-2, as well as adults with natural infection only (n = 200). IgG, IgM, IgA, and IgG subclasses were also quantified.

RESULTS

AZ induces greater Fcγ-receptor-binding (types I, IIa, and IIIa/b) antibodies than SV or natural infection. Previously infected individuals have significantly greater vaccine-induced responses compared to naïve counterparts. Fcγ-receptor-binding is highest among AZ vaccinated individuals with a prior infection, for all receptor types, and substantial complement-fixing activity is only seen among this group. SV induces higher IgM than AZ, but this does not drive better complement-fixing activity. Some SV responses are associated with subject age, whereas AZ responses are not. Importantly, functional antibody responses are well retained against the Omicron BA.1 S protein, being best retained for Fcγ-receptor-1 binding, and are higher for AZ than SV.

CONCLUSIONS

Hybrid immunity, from combined natural exposure and vaccination, generates strong Fc-mediated antibody functions which may contribute to immunity against evolving SARS-CoV-2 variants. Understanding determinants of Fc-mediated functions may enable future vaccines with greater efficacy against different variants.

Current Status and Significance of Additional Vaccination with COVID-19 Vaccine in Japan-Considerations from Antibody Levels from Hybrid Immunity and Public Perceptions

This report examines the evolving role of coronavirus disease 2019 (COVID-19) vaccination in Japan, especially in light of the reduced public concern following the reclassification of COVID-19 as a Category 5 infectious disease in May 2023. With over half the population estimated to have hybrid immunity from prior infections and vaccinations, this report evaluated the necessity and frequency of additional booster doses. Despite strong recommendations from Japanese medical societies to continue vaccination, public skepticism remains owing to financial burdens, adverse reactions, and the perceived limited benefits of frequent boosters. Studies on antibody responses have revealed that individuals with hybrid immunity maintain robust protection with significantly elevated antibody titers that persist over extended periods. Case studies have indicated durable immunity among individuals who have both been vaccinated and experienced breakthrough infections, raising questions about the need for uniform booster policies. This report also discusses the newly approved replicon-type (self-amplifying) vaccines currently available only in Japan, which have generated public and professional debates regarding their efficacy and safety. A more personalized approach to vaccination that takes into account the antibody titers, prior infection history, and individual choices is recommended. Finally, this report underscores the importance of aligning vaccination policies with scientific evidence and public sentiment to optimize COVID-19 countermeasures in Japan.

Tissue-resident memory T cells contribute to protection against heterologous SARS-CoV-2 challenge

New vaccine formulations are based on circulating strains of virus, which have tended to evolve to more readily transmit human to human and to evade the neutralizing antibody response. An assumption of this approach is that ancestral strains of virus will not recur. Recurrence of these strains could be a problem for individuals not previously exposed to ancestral spike protein. Here, we addressed this by infecting mice with recent SARS-CoV-2 variants and then challenging them with a highly pathogenic mouse-adapted virus closely related to the ancestral Wuhan-1 strain (SARS2-N501YMA30). We found that challenged mice were protected from severe disease, despite having low or no neutralizing antibodies against SARS2-N501YMA30. T cell depletion from previously infected mice did not diminish infection against clinical disease, although it resulted in delayed virus clearance in the nasal turbinate and, in some cases, in the lungs. Levels of tissue-resident memory T cells were significantly elevated in the nasal turbinate of previously infected mice compared with that of naive mice. However, this phenotype was not seen in lung tissues. Together, these results indicate that the immune response to newly circulating variants afforded protection against reinfection with the ancestral virus that was in part T cell based.

Ndungu F. Kinetics of naturally induced binding and neutralising anti-SARS-CoV-2 antibody levels and potencies among SARS-CoV-2 infected Kenyans with diverse grades of COVID-19 severity: an observational study

Background

Given the low levels of coronavirus disease 2019 (COVID-19) vaccine coverage in sub-Saharan Africa (sSA), despite high levels of natural severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) exposures, strategies for extending the breadth and longevity of naturally acquired immunity are warranted. Designing such strategies will require a good understanding of naturally acquired immunity.

Methods

We measured whole-spike immunoglobulin G (IgG) and spike-receptor binding domain (RBD) total immunoglobulins (Igs) on 585 plasma samples collected longitudinally over five successive time points within six months of COVID-19 diagnosis in 309 COVID-19 patients. We measured antibody-neutralising potency against the wild-type (Wuhan) SARS-CoV-2 pseudovirus in a subset of 51 patients over three successive time points. Binding and neutralising antibody levels and potencies were then tested for correlations with COVID-19 severities.

Results

Rates of seroconversion increased from day 0 (day of PCR testing) to day 180 (six months) (63.6% to 100 %) and (69.3 % to 97%) for anti-spike-IgG and anti-spike-RBD binding Igs, respectively. Levels of these binding antibodies peaked at day 28 (p<0.01) and were subsequently maintained for six months without significant decay (p>0.99). Similarly, antibody-neutralising potencies peaked at day 28 (p<0.01) but declined by three-fold, six months after COVID-19 diagnosis (p<0.01). Binding antibody levels were highly correlated with neutralising antibody potencies at all the time points analysed (r>0.60, p<0.01). Levels and potencies of binding and neutralising antibodies increased with disease severity.

Conclusions

Most COVID-19 patients generated SARS-CoV-2 specific binding antibodies that remained stable in the first six months of infection. However, the respective neutralising antibodies decayed three-fold by month-six of COVID-19 diagnosis suggesting that they are short-lived, consistent with what has been observed elsewhere in the world. Thus, regular vaccination boosters are required to sustain the high levels of anti-SARS-CoV-2 naturally acquired neutralising antibody potencies in our population.

Deep immunoglobulin repertoire sequencing depicts a comprehensive atlas of spike-specific antibody lineages shared among COVID-19 convalescents

Neutralizing antibodies are a key component in protective humoral immunity against SARS-CoV-2. Currently, available technologies cannot track epitope-specific antibodies in global antibody repertoires. Thus, the comprehensive repertoire of spike-specific neutralizing antibodies elicited by SARS-CoV-2 infection is not fully understood. We therefore combined high-throughput immunoglobulin heavy chain (IgH) repertoire sequencing, and structural and bioinformatics analysis to establish an antibodyomics pipeline, which enables tracking spike-specific antibody lineages that target certain neutralizing epitopes. We mapped the neutralizing epitopes on the spike and determined the epitope-preferential antibody lineages. This analysis also revealed numerous overlaps between immunodominant neutralizing antibody-binding sites and mutation hotspots on spikes as observed so far in SARS-CoV-2 variants. By clustering 2677 spike-specific antibodies with 360 million IgH sequences that we sequenced, a total of 329 shared spike-specific antibody clonotypes were identified from 33 COVID-19 convalescents and 24 SARS-CoV-2-naïve individuals. Epitope mapping showed that the shared antibody responses target not only neutralizing epitopes on RBD and NTD but also non-neutralizing epitopes on S2. The immunodominance of neutralizing antibody response is determined by the occurrence of specific precursors in human naïve B-cell repertoires. We identified that only 28 out of the 329 shared spike-specific antibody clonotypes persisted for at least 12 months. Among them, long-lived IGHV3-53 antibodies are likely to evolve cross-reactivity to Omicron variants through accumulating somatic hypermutations. Altogether, we created a comprehensive atlas of spike-targeting antibody lineages in COVID-19 convalescents and antibody precursors in human naïve B cell repertoires, providing a valuable reference for future vaccine design and evaluation.

Comparison of different T cell assays for the retrospective determination of SARS-CoV-2 infection

It is important to be able to retrospectively determine severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections with high accuracy, both for post-coronavirus disease 2019 (COVID-19) epidemiological studies, and to distinguish between Long COVID and other multi-syndromic diseases that have overlapping symptoms. Although serum antibody levels can be measured to retrospectively diagnose SARS-CoV-2 infections, peptide stimulation of memory T cell responses is a more sensitive approach. This is because robust memory T cells are generated after SARS-CoV-2 infection and persist even after antibodies wane below detectability thresholds. In this study, we compare T cell responses using FluoroSpot-based methods and overnight stimulation of whole blood with SARS-CoV-2 peptides followed by an ELISA. Both approaches have comparable sensitivity and specificity but require different equipment and samples to be used. Furthermore, the elimination of peptides that cross-react with other coronaviruses increases the assay specificity but trades off some sensitivity. Finally, this approach can be used on archival, cryopreserved PBMCs. This work shows comparative advantages for several methods to measure SARS-CoV-2 T cell responses that could be utilized by any laboratory studying the effects of the coronavirus disease 2019 pandemic.

Immune evasion after SARS-CoV-2 Omicron BA.5 and XBB.1.9 endemic observed from Guangdong Province, China from 2022 to 2023

BACKGROUND

From 2022 to 2023, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) caused by Omicron variants spread rapidly in Guangdong Province, resulting in over 80% of the population being infected.

RESULTS

To investigate the levels of neutralizing antibodies (NAbs) in individuals following the rapid pandemic and to evaluate the cross-protection against currently circulating variants of SARS-CoV-2 in China, neutralization assay and magnetic particle chemiluminescence method were used to test the 117 serum samples from individuals who had recovered 4 weeks post-infection. The results indicated that the levels of NAbs against prototype and Omicron variants BA.5 were significantly higher than those against Omicron variants BQ.1, XBB.1.1, XBB.1.9, XBB.1.16 and EG.5, regardless of whether the infection was primary or secondary.

CONCLUSIONS

The cross-protection provided by NAbs induced by prototype and Omicron BA.5 variants was limited when challenged by BQ.1, XBB.1.1, XBB.1.9, XBB.1.16 and EG.5 variants. This indicates that we should pay more attention to the risk of multiple infection from any novel Omicron variants that may emerge in the near future.

Profiling serum immunodominance following SARS-CoV-2 primary and breakthrough infection reveals distinct variant-specific epitope usage and immune imprinting

Over the course of the COVID-19 pandemic, variants have emerged with increased mutations and immune evasive capabilities. This has led to breakthrough infections (BTI) in vaccinated individuals, with a large proportion of the neutralizing antibody response targeting the receptor binding domain (RBD) of the SARS-CoV-2 Spike glycoprotein. Immune imprinting, where prior exposure of the immune system to an antigen can influence the response to subsequent exposures, and its role in a population with heterogenous exposure histories has important implications in future vaccine design. Here, we develop an accessible approach to map epitope immunodominance of the neutralizing antibody response in sera. By using a panel of mutant Spike proteins in a pseudotyped virus neutralization assay, we observed distinct epitope usage in convalescent donors infected during wave 1, or infected with the Delta, or BA.1 variants, highlighting the antigenic diversity of the variant Spikes. Analysis of longitudinal serum samples taken spanning 3 doses of COVID-19 vaccine and subsequent breakthrough infection, showed the influence of immune imprinting from the ancestral-based vaccine, where reactivation of existing B cells elicited by the vaccine resulted in the enrichment of the pre-existing epitope immunodominance. However, subtle shifts in epitope usage in sera were observed following BTI by Omicron sub-lineage variants. Antigenic distance of Spike, time after last exposure, and number of vaccine boosters may play a role in the persistence of imprinting from the vaccine. This study provides insight into RBD neutralizing epitope usage in individuals with varying exposure histories and has implications for design of future SARS-CoV-2 vaccines.

Identification of virus epitopes and reactive T-cell receptors from memory T cells without peptide synthesis

Identifying epitopes and their corresponding T-cell receptor (TCR) sequences is crucial in the face of rapidly mutating viruses. Peptide synthesis is often required to confirm the exact epitope sequences, which is time-consuming and expensive. In this study, we introduce a scalable workflow to identify the exact sequences of virus epitopes and reactive TCRs targeting the epitopes from memory T cells. Following the narrowing down of epitopes to specific regions via the tandem minigene (TMG) system, our workflow incorporates the utilization of peptide-major histocompatibility complex-displaying yeasts (pMHC-displaying yeasts) to rapidly screen immunogenic epitopes' precise sequences, obviating the necessity for the chemical synthesis of peptides. Focusing on SARS-CoV-2, we identify the precise sequences of reactive TCRs, targeting conserved epitopes across the Coronaviridae family, from the blood of COVID-19-recovered individuals over 8 months. Notably, we reveal that at least 75% (6/8) of the tested donors harbor T cells targeting a shared epitope, KTFPPTEPK, derived from the N protein. Furthermore, several identified TCRs exhibit cross-reactivity to mutant epitopes, suggesting a potential mechanism for sustained T-cell responses against emerging SARS-CoV-2 variants.

Antibody response to SARS-CoV-2 natural and breakthrough infection in patients undergoing maintenance hemodialysis: A prospective cohort study over 4 months

Background

Patients undergoing maintenance hemodialysis (MHD) are susceptible to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. However, the antibody response of these patients to natural and breakthrough infections remains poorly understood.

Methods

Between January 15, 2023, and February 15, 2023, a total of 53 patients undergoing MHD and diagnosed with SARS-CoV-2 infection at The Affiliated Hospital of Hangzhou Normal University were enrolled. They were categorized into the natural (n = 40) and breakthrough infection groups (n = 13) based on their vaccination status before infection. Comprehensive data, including basic clinical information, vaccination status, and routine post-infection blood parameters, were collected from all participants. Blood specimens were drawn monthly after infection, and SARS-CoV-2 receptor-binding domain (RBD) immunoglobulin (Ig) G and IgM tests were conducted. The study included continuous follow-up over 4 months.

Results

During the acute phase of infection, the SARS-CoV-2 RBD IgM positivity was 5 % in patients undergoing MHD who were naturally infected and 15.4 % in those with breakthrough infections. Four months after infection, SARS-CoV-2 RBD IgG positivity in patients with natural and breakthrough infection was 77.5 % and 100 %, respectively. Patients undergoing MHD with breakthrough infection exhibited higher SARS-CoV-2 RBD IgG titers (751.21 signal-to cutoff ratio, S/CO [interquartile range, IQR, 30.54-1173.63]) than those with natural infections (3.43 S/CO [IQR, 1.12-15.6]) (p < 0.0001). No significant differences were observed in SARS-CoV-2 RBD IgG between males and females or among those aged <70 and ≥70 years. Patients who received three doses of the inactivated vaccine produced significantly higher SARS-CoV-2 RBD IgG levels after infection than those who received one or two doses; these differences were significant.

Conclusions

Although patients undergoing MHD exhibit a low rate of SARS-CoV-2 RBD IgM positivity following infection, those vaccinated with inactivated vaccines can generate elevated SARS-CoV-2 RBD IgG levels, particularly those who receive three doses.

SARS-CoV-2-Specific T-Cell as a Potent Therapeutic Strategy against Immune Evasion of Emerging COVID-19 Variants

Despite advances in vaccination and therapies for coronavirus disease, challenges remain due to reduced antibody longevity and the emergence of virulent variants like Omicron (BA.1) and its subvariants (BA.1.1, BA.2, BA.3, and BA.5). This study explored the potential of adoptive immunotherapy and harnessing the protective abilities using virus-specific T cells (VSTs). Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) VSTs were generated by stimulating donor-derived peripheral blood mononuclear cells with spike, nucleocapsid, and membrane protein peptide mixtures. Phenotypic characterization, including T-cell receptor (TCR) vβ and pentamer analyses, was performed on the ex vivo-expanded cells. We infected human leukocyte antigen (HLA)-partially matched human Calu-3 cells with various authentic SARS-CoV-2 strains in a Biosafety Level 3 facility and co-cultured them with VSTs. VSTs exhibited a diverse TCR vβ repertoire, confirming their ability to target a broad range of SARS-CoV-2 antigens from both the ancestral and mutant strains, including Omicron BA.1 and BA.5. These ex vivo-expanded cells exhibited robust cytotoxicity and low alloreactivity against HLA-partially matched SARS-CoV-2-infected cells. Their cytotoxic effects were consistent across variants, targeting conserved spike and nucleocapsid epitopes. Our findings suggest that third-party partial HLA-matching VSTs could counter immune-escape mechanisms posed by emerging variants of concern.

Safety and Immunogenicity Study of a Bivalent Vaccine for Combined Prophylaxis of COVID-19 and Influenza in Non-Human Primates

BACKGROUND

Influenza and SARS-CoV-2 viruses are two highly variable pathogens. We have developed a candidate bivalent live vaccine based on the strain of licensed A/Leningrad/17-based cold-adapted live attenuated influenza vaccine (LAIV) of H3N2 subtype, which expressed SARS-CoV-2 immunogenic T-cell epitopes. A cassette encoding fragments of S and N proteins of SARS-CoV-2 was inserted into the influenza NA gene using the P2A autocleavage site. In this study, we present the results of preclinical evaluation of the developed bivalent vaccine in a non-human primate model.

METHODS

Rhesus macaques (Macaca mulatta) (n = 3 per group) were immunized intranasally with 7.5 lg EID50 of the LAIV/CoV-2 bivalent vaccine, a control non-modified H3N2 LAIV or a placebo (chorioallantoic fluid) using a sprayer device, twice, with a 28-day interval. The blood samples were collected at days 0, 3, 28 and 35 for hematological and biochemical assessment. Safety was also assessed by monitoring body weight, body temperature and clinical signs of the disease. Immune responses to influenza virus were assessed both by determining serum antibody titers in hemagglutination inhibition assay, microneutralization assay and IgG ELISA. T-cell responses were measured both to influenza and SARS-CoV-2 antigens using ELISPOT and flow cytometry. Three weeks after the second immunization, animals were challenged with 105 PFU of Delta SARS-CoV-2. The body temperature, weight and challenge virus shedding were monitored for 5 days post-challenge. In addition, virus titers in various organs and histopathology were evaluated on day 6 after SARS-CoV-2 infection.

RESULTS

There was no toxic effect of the immunizations on the hematological and coagulation hemostasis of animals. No difference in the dynamics of the average weight and thermometry results were found between the groups of animals. Both LAIV and LAIV/CoV-2 variants poorly replicated in the upper respiratory tract of rhesus macaques. Nevertheless, despite this low level of virus shedding, influenza-specific serum IgG responses were detected in the group of monkeys immunized with the LAIV/CoV-2 bivalent but not in the LAIV group. Furthermore, T-cell responses to both influenza and SARS-CoV-2 viruses were detected in the LAIV/CoV-2 vaccine group only. The animals were generally resistant to SARS-CoV-2 challenge, with minimal virus shedding in the placebo and LAIV groups. Histopathological changes in vaccinated animals were decreased compared to the PBS group, suggesting a protective effect of the chimeric vaccine candidate.

CONCLUSIONS

The candidate bivalent vaccine was safe and immunogenic for non-human primates and warrants its further evaluation in clinical trials.

SARS-CoV-2 antibody levels and long COVID occurrence in blood donors

BACKGROUND

Long COVID is a common condition lacking consensus definition; determinants remain incompletely understood. Characterizing immune profiles associated with long COVID could support the development of preventive and therapeutic strategies.

METHODS

We used a survey to investigate blood donors' infection/vaccination history and acute/persistent symptoms following COVID-19. The prevalence of long COVID was evaluated using self-report and an adapted definition from the RECOVER study. We evaluated factors associated with long COVID, focusing on anti-spike and anti-nucleocapsid SARS-CoV-2 antibodies. Lastly, we investigated long COVID clinical subphenotypes using hierarchical clustering.

RESULTS

Of 33,610 participants, 16,003 (48%) reported having had COVID-19; 1853 (12%) had self-reported long COVID, 685 (4%) met an adapted RECOVER definition, and 2050 (13%) met at least one definition. Higher anti-nucleocapsid levels measured 12-24 weeks post-infection were associated with higher risk of self-reported and RECOVER long COVID. Higher anti-spike IgG levels measured 12-24 weeks post-infection were associated with lower risk of self-reported long COVID. Higher total anti-spike measured 24-48 weeks post-infection was associated with lower risk of RECOVER long COVID. Cluster analysis identified four clinical subphenotypes; patterns included neurological and psychiatric for cluster 1; neurological and respiratory for cluster 2; multi-systemic for cluster 3; and neurological for cluster 4.

DISCUSSION

Long COVID prevalence in blood donors varies depending on the adopted definition. Anti-SARS-CoV-2 antibodies were time-dependently associated with long COVID; higher anti-nucleocapsid levels were associated with higher risk; and higher anti-spike levels were associated with lower risk of long COVID. Different underlying pathophysiologic mechanisms may be associated with distinct clinical subphenotypes.

Characteristics of Immunogenicity against SARS-CoV-2 in a Community-Based Model of Care during the Fourth Wave of COVID-19 Outbreak in Ho Chi Minh City

PURPOSE

Although some immune protection from close contact with individuals who have coronavirus disease 2019 (COVID-19) has been documented, there is limited data on the seroprevalence of antibodies against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in individuals who were in lockdown with confirmed COVID-19 cases. This study investigated immunogenicity against SARS-CoV-2 in household members and people who lived near home-quarantined patients with COVID-19.

MATERIALS AND METHODS

This cross-sectional study was conducted during the community-based care that took place during lockdowns in District 10, Ho Chi Minh City, Vietnam from July to September 2021. SARS-CoV-2 antibody levels were determined in index cases of COVID-19, household contacts, and a no-contact group from the same area.

RESULTS

A total of 770 participants were included (355 index cases, 103 household contacts, and 312 no contacts). All index cases were unvaccinated, but >90% of individuals in the household and no-contact groups had received ≥1 vaccine dose. SARS-CoV-2 neutralizing antibodies (Nabs) were present in >77% of unvaccinated index cases versus 64%/65.4% in the household/no-contact groups (p=0.001). Antibody concentrations in unvaccinated index cases were significantly higher than those in household contacts and no contacts, with no difference between the latter groups. In all cases, antibody levels declined markedly ≥6 weeks after infection, and failed to persist beyond this time in the household and no-contact groups.

CONCLUSION

Community-based care may have helped to create community immunogenicity, but Nabs did not persist, highlighting a need for vaccination for all individuals before, or from 6 weeks after, infection with SARS-CoV-2.

Development of T cell antigen-based human coronavirus vaccines against nAb-escaping SARS-CoV-2 variants

Currently approved vaccines have been successful in preventing the severity of COVID-19 and hospitalization. These vaccines primarily induce humoral immune responses; however, highly transmissible and mutated variants, such as the Omicron variant, weaken the neutralization potential of the vaccines, thus, raising serious concerns about their efficacy. Additionally, while neutralizing antibodies (nAbs) tend to wane more rapidly than cell-mediated immunity, long-lasting T cells typically prevent severe viral illness by directly killing infected cells or aiding other immune cells. Importantly, T cells are more cross-reactive than antibodies, thus, highly mutated variants are less likely to escape lasting broadly cross-reactive T cell immunity. Therefore, T cell antigen-based human coronavirus (HCoV) vaccines with the potential to serve as a supplementary weapon to combat emerging SARS-CoV-2 variants with resistance to nAbs are urgently needed. Alternatively, T cell antigens could also be included in B cell antigen-based vaccines to strengthen vaccine efficacy. This review summarizes recent advancements in research and development of vaccines containing T cell antigens or both T and B cell antigens derived from proteins of SARS-CoV-2 variants and/or other HCoVs based on different vaccine platforms.

Genetic, Clinical, Epidemiological, and Immunological Profiling of IgG Response Duration after SARS-CoV-2 Infection

The IgG response against SARS-CoV-2 infection can persist for over six months (long response; LR). However, among 30% of those infected, the duration can be as short as three months or less (short response; SR). The present study assembled serological data on the anti-SARS-CoV-2 IgG response duration of two previous studies and integrated these results with the plasmatic cytokine levels and genetic profile of 10 immune-relevant SNPs that were also previously published, along with the plasmatic total IgG, IgA, and IgM levels, allowing for the genetic, clinical, immunological, and epidemiological aspects of the post-COVID-19 IgG response duration to be understood. The SR was associated with previous mild acute COVID-19 and with an SNP (rs2228145) in IL6R related to low gene expression. Additionally, among the SR subgroup, no statistically significant Spearman correlations were observed between the plasma levels of IL-17A and the Th17 regulatory cytokines IFN-γ (rs = 0.2399; p = 0.1043), IL-4 (rs = 0.0273; p = 0.8554), and IL-2 (rs = 0.2204; p = 0.1365), while among the LR subgroup, weaker but statistically significant Spearman correlations were observed between the plasma levels of IL-17A and IFN-γ (rs = 0.3873; p = 0.0016), IL-4 (rs = 0.2671; p = 0.0328), and IL-2 (rs = 0.3959; p = 0.0012). These results suggest that the Th17 response mediated by the IL-6 pathway has a role in the prolonged IgG response to SARS-CoV-2 infection.

Dynamics of anti-SARS-CoV-2 IgG antibody responses following breakthrough infection and the predicted protective efficacy: A longitudinal community-based population study in China

OBJECTIVES

To assess the dynamics of the anti-SARS-CoV-2 IgG antibody levels and their efficacy against COVID-19.

METHODS

We conducted a longitudinal serological analysis of 852 breakthrough COVID-19 infections among the community-based population in Yichang, China. Anti-SARS-CoV-2 IgG levels were measured by chemiluminescence at approximately 3, 4, and 9 months after infection. A linear mixed model predicted IgG antibody decline over 18 months. The effectiveness of antibodies in preventing symptomatic and severe infections was determined using an existing meta-regression model.

RESULTS

IgG antibodies slowly declined after breakthrough infections. Initially high at around 3 months (339.44 AU/mL, IQR: 262.78-382.95 AU/mL), levels remained significant at 9 months (297.74 AU/mL, IQR: 213.22-360.62 AU/mL). The elderly (≥60 years) had lower antibody levels compared to the young (<20 years) (P < 0.001). The protective efficacy of antibodies against symptomatic and severe infections was lower in the elderly (≥60 years) (78.34% and 86.33%) compared to the young (<20 years) (96.56% and 98.75%) after 1 year.

CONCLUSION

The study indicated a slow decline in anti-SARS-CoV-2 IgG antibodies, maintaining considerable efficacy for over 1 year. However, lower levels in the elderly suggest reduced protective effects, underscoring the need for age-specific vaccination strategies.

Strategies to determine positive anti-SARS-CoV-2 memory T lymphocyte response during the evolution of an epidemic

During SARS-CoV-2 pandemic, the assessment of immune protection of people at risk of severe infection was an important goal. The appearance of VOCs (Variant of Concern) highlighted the limits of evaluating immune protection through the humoral response. While the humoral response partly loses its neutralizing activity, the anti-SARS-CoV-2 memory T cell response strongly cross protects against VOCs becoming an indispensable tool to assess immune protection. We compared two techniques available in laboratory to evaluate anti-SARS-CoV-2 memory T cell response in a cohort of infected or vaccinated patients with different levels of risk to develop a severe disease: the ELISpot assay and the T-Cell Lymphocyte Proliferation Assay respectively exploring IFNγ production and cell proliferation. We showed that the ELISpot assay detected more anti-Spike memory T cell response than the Lymphocyte Proliferation Assay. We next observed that the use of two different suppliers as antigenic source in the ELISpot assay did not affect the detection of anti-Spike memory T cell response. Finally, we explored a new approach for defining the positivity threshold, using unsupervised mixed Gaussian modeling, challenging the traditional ROC curve used by the supplier. That will be helpful in endemic situation where it could be difficult to recruit "negative" patients.

Vitamin D supplementation and calcium: Many-faced gods or nobody in fighting against Corona Virus Disease 2019

In December 2019, Corona Virus Disease 2019 (COVID-19) was first identified and designated as a pandemic in March 2020 due to rapid spread of the virus globally. At the beginning of the pandemic, only a few treatment options, mainly focused on supportive care and repurposing medications, were available. Due to its effects on immune system, vitamin D was a topic of interest during the pandemic, and researchers investigated its potential impact on COVID-19 outcomes. However, the results of studies about the impact of vitamin D on the disease are inconclusive. In the present narrative review, different roles of vitamin D regarding the COVID-19 have been discussed to show that vitamin D supplementation should be recommended carefully.

Deciphering Fc-effector functions against SARS-CoV-2

Major efforts were deployed to study the antibody response against SARS-CoV-2. Antibodies neutralizing SARS-CoV-2 have been extensively studied in the context of infections, vaccinations, and breakthrough infections. Antibodies, however, are pleiotropic proteins that have many functions in addition to neutralization. These include Fc-effector functions such as antibody-dependent cellular cytotoxicity (ADCC) and antibody-dependent cellular phagocytosis (ADCP). Although important to combat viral infections, these Fc-effector functions were less studied in the context of SARS-CoV-2 compared with binding and neutralization. This is partly due to the difficulty in developing reliable assays to measure Fc-effector functions compared to antibody binding and neutralization. Multiple assays have now been developed and can be used to measure different Fc-effector functions. Here, we review these assays and what is known regarding anti-SARS-CoV-2 Fc-effector functions. Overall, this review summarizes and updates our current state of knowledge regarding anti-SARS-CoV-2 Fc-effector functions.

Recombinant OC43 SARS-CoV-2 spike replacement virus: An improved BSL-2 proxy virus for SARS-CoV-2 neutralization assays

We generated a replication-competent OC43 human seasonal coronavirus (CoV) expressing the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike in place of the native spike (rOC43-CoV2 S). This virus is highly attenuated relative to OC43 and SARS-CoV-2 in cultured cells and animals and is classified as a biosafety level 2 (BSL-2) agent by the NIH biosafety committee. Neutralization of rOC43-CoV2 S and SARS-CoV-2 by S-specific monoclonal antibodies and human sera is highly correlated, unlike recombinant vesicular stomatitis virus-CoV2 S. Single-dose immunization with rOC43-CoV2 S generates high levels of neutralizing antibodies against SARS-CoV-2 and fully protects human ACE2 transgenic mice from SARS-CoV-2 lethal challenge, despite nondetectable replication in respiratory and nonrespiratory organs. rOC43-CoV2 S induces S-specific serum and airway mucosal immunoglobulin A and IgG responses in rhesus macaques. rOC43-CoV2 S has enormous value as a BSL-2 agent to measure S-specific antibodies in the context of a bona fide CoV and is a candidate live attenuated SARS-CoV-2 mucosal vaccine that preferentially replicates in the upper airway.

SARS-CoV-2 Variants and COVID-19 in Bangladesh-Lessons Learned

The coronavirus infectious disease-2019 (COVID-19) in Bangladesh is a paradigm for how one of the most densely populated countries in the world, with 1270 people per square kilometer, managed to cope with the COVID-19 pandemic under extraordinary circumstances. This review highlights the SARS-CoV-2 variants in Bangladesh and the timeline of their detection in the context of the global experience with the management of vaccination and natural SARS-CoV-2 infection. The motivation to overcome the COVID-19 vaccine dilemma and track Bangladeshi SARS-CoV-2 sub-variants underscores the potential for a low-income country to excel in international medical science, despite having stressed health care services and limited availability of resources for SARS-CoV-2 testing and gene sequencing.

SARS-CoV-2 seroprevalence among Beninese pregnant women in the third year of the pandemic

BACKGROUND

Pregnant women are a vulnerable population to COVID-19 given an increased susceptibility to severe SARS-CoV-2 infection and pregnancy complications. However, few SARS-CoV-2 serological surveys have been performed among this population to assess the extent of the infection in sub-Saharan countries. The objectives of this study were to determine SARS-CoV-2 seroprevalence among Beninese pregnant women, to identify spatial seropositivity clusters and to analyse factors associated with the infection.

METHODS

A cross-sectional study including women in their third trimester of pregnancy attending the antenatal care (ANC) clinics at Allada (south Benin) and Natitingou (north Benin) was conducted. Rapid diagnostic tests (RDT) for detection of IgG/IgM against the SARS-CoV-2 spike protein were performed using capillary blood. Seroprevalence of SARS-CoV-2 antibodies and associations between SARS-CoV-2 serostatus and maternal characteristics were analyzed by multivariate logistic regression. Spatial analyses were performed using the spatial scan statistics to identify spatial clusters of SARS-CoV-2 infection.

RESULTS

A total of 861 pregnant women were enrolled between May 4 and June 29, 2022. 58/861 (6.7%) participants reported having received COVID-19 vaccine. None of the participants had been diagnosed with COVID-19 during their pregnancy. SARS-CoV-2 antibodies were detected in 607/802 (75.7%; 95% CI 72.56%-78.62%) of unvaccinated participants. Several urban and rural spatial clusters of SARS-CoV-2 cases were identified in Allada and one urban spatial cluster was identified in Natitingou. Unvaccinated participants from Allada with at least one previous morbidity were at a three-times higher risk of presenting SARS-CoV-2 antibodies (OR = 2.89; 95%CI 1.19%-7.00%).

CONCLUSION

Three out of four pregnant women had SARS-CoV-2 antibodies, suggesting a high virus circulation among pregnant women in Benin, while COVID-19 vaccination coverage was low. Pregnant women with comorbidities may be at increased risk of SARS-CoV-2 infection. This population should be prioritized for COVID-19 diagnosis and vaccination in order to prevent its deleterious effects.

TRIAL REGISTRATION

NCT06170320 (retrospectively registered on December 21, 2023).

SARS-CoV-2 in Mozambican primary school-aged children at Maputo City and Province: a cross-sectional study from a low-income country

BACKGROUND

Seroprevalence studies provide information on the true extent of infection and capture demographic and geographic differences, indicating the level of immunity against Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2). We sought to provide local evidence of SARS-CoV-2 exposure in school-aged children during in-class teaching in Maputo City and Province, Mozambique.

METHODS

Between August and November 2022, we performed a cross-sectional study in school-aged children in four schools in rural, peri-urban, and urban areas of Maputo City and Province. A point-of-care test was used to evaluate SARS-CoV-2 antigens and anti-SARS-CoV-2-specific immunoglobulin M (IgM) and immunoglobulin G (IgG) antibodies. Descriptive statistics were used to estimate the prevalence of the antigens and antibodies. Multiple logistic regression models were used to estimate the adjusted odds ratio (AOR) for the factors associated with anti-SARS-CoV-2 antibodies.

RESULTS

A total of 736 school-aged children were analyzed. The prevalence of the SARS-CoV-2 antigen was 0.5% (4/736). The prevalence of SARS-CoV-2 antigens was 0.0% (0/245), 0.8% (2/240) and 0.8% (2/251), in the rural, peri-urban and urban areas respectively. The overall seroprevalence of the anti-SARS-CoV-2 antibodies (IgG or IgM) was 80.7% (594/736). In rural area anti-SARS-CoV-2 IgG or IgM antibodies were detected in 76.7% (188/245), while in peri-urban area they were detected in 80.0% (192/240) and in urban area they were detected in 85.3% (214/251). In the adjusted logistic regression model, school-aged children from the urban area were more likely to have anti-SARS-CoV-2 IgG or IgM antibodies than were school-aged children from the rural area (adjusted odds ratio: 1.679; 95% CI: 1.060-2.684; p-value = 0.028).

CONCLUSIONS

During the in-class teaching period, active SARS-CoV-2 cases in school-aged children were observed. More than half of the school-aged children were exposed to SARS-CoV-2, and SARS-CoV-2 was significantly more common in the schools at the urban area than in the school in the rural area at Maputo City and Province.

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.

Anti-SARS-CoV-2 Neutralizing Responses in Various Populations: Use of a Rapid Surrogate Lateral Flow Assay and Correlations with Anti-RBD Antibody Levels

BACKGROUND

After the global COVID-19 crisis, understanding post-infectious immunity and vaccine efficacy remains crucial. This study aims to assess anti-SARS-CoV-2 immunity through a quantitative analysis of anti-receptor-binding domain (RBD) antibodies and rapid functional testing of the neutralizing humoral response.

METHODS

A retrospective analysis was conducted on samples from various cohorts, including partially vaccinated, fully vaccinated, post-COVID/no-vaccination, and post-COVID/vaccination individuals with various immune-competency statuses. The anti-RBD antibodies were measured using an automated chemiluminescence assay, while the neutralizing antibodies' (NAbs') activity was assessed through the lateral flow ichroma COVID-19 nAb test (LFT), a surrogate neutralization assay.

RESULTS

The analysis revealed various levels of anti-RBD antibodies and seroneutralization responses across cohorts, with the post-COVID/vaccination group demonstrating the most robust protection. A correlation between anti-RBD antibodies and seroneutralization was observed, albeit with varying strength depending on the subgroup analyzed. Longitudinal assessment following natural infection showed an initial surge followed by a decline in both measures. A cutoff of 3.0 log10 BAU/mL was established to predict significant seroneutralization.

CONCLUSIONS

The ichroma™ COVID-19 nAb test displayed high specificity and emerged as a valuable tool for monitoring anti-SARS-CoV-2 immunity. These findings contribute to understand the antibody response dynamics and underscore the potential of rapid tests in predicting protection against SARS-CoV-2 infection.

Determinants of Systemic SARS-CoV-2-Specific Antibody Responses to Infection and to Vaccination: A Secondary Analysis of Randomised Controlled Trial Data

SARS-CoV-2 infections elicit antibodies against the viral spike (S) and nucleocapsid (N) proteins; COVID-19 vaccines against the S-protein only. The BCG-Corona trial, initiated in March 2020 in SARS-CoV-2-naïve Dutch healthcare workers, captured several epidemic peaks and the introduction of COVID-19 vaccines during the one-year follow-up. We assessed determinants of systemic anti-S1 and anti-N immunoglobulin type G (IgG) responses using trial data. Participants were randomised to BCG or placebo vaccination, reported daily symptoms, SARS-CoV-2 test results, and COVID-19 vaccinations, and donated blood for SARS-CoV-2 serology at two time points. In the 970 participants, anti-S1 geometric mean antibody concentrations (GMCs) were much higher than anti-N GMCs. Anti-S1 GMCs significantly increased with increasing number of immune events (SARS-CoV-2 infection or COVID-19 vaccination): 104.7 international units (IU)/mL, 955.0 IU/mL, and 2290.9 IU/mL for one, two, and three immune events, respectively (p < 0.001). In adjusted multivariable linear regression models, anti-S1 and anti-N log10 concentrations were significantly associated with infection severity, and anti-S1 log10 concentration with COVID-19 vaccine type/dose. In univariable models, anti-N log10 concentration was also significantly associated with acute infection duration, and severity and duration of individual symptoms. Antibody concentrations were not associated with long COVID or long-term loss of smell/taste.

Prevalence, under-reporting, and epidemiological surveillance of COVID-19 in the Araguaína City of Brazil

Asymptomatic and underreported individuals remain a source of coronafig disease 2019 (COVID-19) transmission to others. Data on the prevalence and epidemiological factors influencing transmission are fundamental for establishing control measures, especially in vulnerable regions such as the Amazon. This study aimed to determine the point prevalence and active infection of COVID-19 among the population in Araguaína, a Brazilian city located in the Amazon region, analyzed the socioeconomic and behavioral variables of a statistically representative sample of this population using an epidemiological survey, and identify the viral genomic diversity in the region. During the sixth epidemiological week of 2021 (February 8 to 12), samples of 497 inhabitants of the municipality asymptomatic for respiratory syndromes underwent reverse transcription-quantitative polymerase chain reaction and serological tests (immunoglobulin M and immunoglobulin G). A questionnaire collated data on socioeconomic factors, prevention measures, and health status history. The active infection rate was 6.2%, and the prevalence was 13.5% of the study population. Active infection cases were under-reported; each reported positive case represented 14-28 under-reported cases. Lineages P.2, P.1, and B.1.1 were detected. Working from home was a protective factor against the infection, and clinical signs of fever, dry cough, and loss of taste or smell were associated with testing positive (p <0.05). A descriptive analysis of the indicators revealed that the entire population was susceptible to the disease. Intensified vaccination strategies are required regardless of socioeconomic factors, health conditions, and preventive measures. Implementation of objective, comprehensive, and efficient management tools to minimize the spread of COVID-19 in this municipality can serve as a model for other regions of Brazil.

Increase in antibody titer and change over time associated with severe acute respiratory syndrome coronavirus 2 infection after mRNA vaccination: Consideration of the significance of additional vaccination

Key Clinical Message

Most Japanese patients naturally infected with COVID-19 were infected after mRNA vaccination, and many maintained high antibody titers due to hybrid immunity. The significance of additional vaccination in hybrid-immunized cases is highly questionable.

Abstract

Spontaneous infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) after mRNA vaccination causes a marked increase in antibody titer because of the combined effect of vaccine and infection ("hybrid immunity"). In this study, we discuss the significance of the mRNA vaccine booster inoculation that has been repeatedly performed in Japan. We describe the temporal trends of antibody titers in cases in which antibody titers were markedly increased by hybrid immunization. The antibody titer increased with hybrid immunization and tended to decrease with time. However, several cases maintained high antibody titers for approximately 1 year after coronavirus disease 2019 (COVID-19) diagnosis, even without booster vaccination. Most Japanese patients naturally infected with COVID-19 were infected after mRNA vaccination, and many maintained high antibody titers due to hybrid immunity. The significance of additional vaccination in hybrid-immunized cases is highly questionable regarding cost-effectiveness and risk-benefit.

COVID-19 seroprevalence cohort survey among health care workers and their household members in Kinshasa, DR Congo, 2020-2022

INTRODUCTION

Serological surveys offer the most direct measurement to define the immunity status for numerous infectious diseases, such as COVID-19, and can provide valuable insights into understanding transmission patterns. This study describes seroprevalence changes over time in the context of the Democratic Republic of Congo, where COVID-19 case presentation was apparently largely oligo- or asymptomatic, and vaccination coverage remained extremely low.

METHODS

A cohort of 635 health care workers (HCW) from 5 health zones of Kinshasa and 670 of their household members was interviewed and sampled in 6 rounds between July 2020 and January 2022. At each round, information on risk exposure and a blood sample were collected. Serology was defined as positive when binding antibodies against SARS-CoV-2 spike and nucleocapsid proteins were simultaneously present.

RESULTS

The SARS-CoV-2 antibody seroprevalence was high at baseline, 17.3% (95% CI 14.4-20.6) and 7.8% (95% CI 5.5-10.8) for HCW and household members, respectively, and fluctuated over time, between 9% and 62.1%. Seropositivity was heterogeneously distributed over the health zones (p < 0.001), ranging from 12.5% (95% CI 6.6-20.8) in N'djili to 33.7% (95% CI 24.6-43.8) in Bandalungwa at baseline for HCW. Seropositivity was associated with increasing rounds adjusted Odds Ratio (aOR) 1.75 (95% CI 1.66-1.85), with increasing age aOR 1.11 (95% CI 1.02-1.20), being a female aOR 1.35 (95% CI 1.10-1.66) and being a HCW aOR 2.38 (95% CI 1.80-3.14). There was no evidence that HCW brought the COVID-19 infection back home, with an aOR of 0.64 (95% CI 0.46-0.91) of seropositivity risk among household members in subsequent surveys. There was seroreversion and seroconversion over time, and HCW had a lower risk of seroreverting than household members (aOR 0.60 (95% CI 0.42-0.86)).

CONCLUSION

SARS-CoV-2 IgG antibody levels were high and dynamic over time in this African setting with low clinical case rates. The absence of association with health profession or general risk behaviors and with HCW positivity in subsequent rounds in HH members, shows the importance of the time-dependent, and not work-related, force of infection. Cohort seroprevalence estimates in a 'new disease' epidemic seem insufficient to guide policy makers for defining control strategies.

Potential Usefulness of IgA for the Early Detection of SARS-CoV-2 Infection: Comparison With IgM

Serological testing can be a powerful complementary approach to achieve timely diagnosis of severe acute respiratory coronavirus 2 (SARS-CoV-2) infection, along with nucleic acid detection. Immunoglobulin (Ig) A antibodies are less frequently utilized to detect SARS-CoV-2 infection than IgM and IgG antibodies, even though IgA antibodies play an important role in protective immunity against SARS-CoV-2. This review discusses the differences in kinetics and assay performance between IgA and IgM antibodies and the factors influencing antibody responses. It highlights the potential usefulness of analyzing IgA antibodies for the early detection of SARS-CoV-2 infection. The early appearance of IgA and the high sensitivity of IgA-based immunoassays can aid in diagnosing coronavirus disease 2019. However, because of cross-reactivity, it is important to recognize the only moderate specificity of the early detection of SARS-CoV-2 IgA antibodies against spike antigens. Either the analysis of antibodies targeting the nucleocapsid antigen or a combination of antibodies against the nucleocapsid and spike antigens may strengthen the accuracy of serological evaluation.

Perturbations of the T-cell receptor repertoire in response to SARS-CoV-2 in immunocompetent and immunocompromised individuals

BACKGROUND

Functional T-cell responses are essential for virus clearance and long-term protection after severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, whereas certain clinical factors, such as older age and immunocompromise, are associated with worse outcome.

OBJECTIVE

We sought to study the breadth and magnitude of T-cell responses in patients with coronavirus disease 2019 (COVID-19) and in individuals with inborn errors of immunity (IEIs) who had received COVID-19 mRNA vaccine.

METHODS

Using high-throughput sequencing and bioinformatics tools to characterize the T-cell receptor β repertoire signatures in 540 individuals after SARS-CoV-2 infection, 31 IEI recipients of COVID-19 mRNA vaccine, and healthy controls, we quantified HLA class I- and class II-restricted SARS-CoV-2-specific responses and also identified several HLA allele-clonotype motif associations in patients with COVID-19, including a subcohort of anti-type 1 interferon (IFN-1)-positive patients.

RESULTS

Our analysis revealed that elderly patients with COVID-19 with critical disease manifested lower SARS-CoV-2 T-cell clonotype diversity as well as T-cell responses with reduced magnitude, whereas the SARS-CoV-2-specific clonotypes targeted a broad range of HLA class I- and class II-restricted epitopes across the viral proteome. The presence of anti-IFN-I antibodies was associated with certain HLA alleles. Finally, COVID-19 mRNA immunization induced an increase in the breadth of SARS-CoV-2-specific clonotypes in patients with IEIs, including those who had failed to seroconvert.

CONCLUSIONS

Elderly individuals have impaired capacity to develop broad and sustained T-cell responses after SARS-CoV-2 infection. Genetic factors may play a role in the production of anti-IFN-1 antibodies. COVID-19 mRNA vaccines are effective in inducing T-cell responses in patients with IEIs.

Development of a colloidal gold-based immunochromatographic assay for rapid detection of nasal mucosal secretory IgA against SARS-CoV-2

Introduction

Infection with SARS-CoV-2 begins in the upper respiratory tract and can trigger the production of mucosal spike-specific secretory IgA (sIgA), which provides protection against reinfection. It has been recognized that individuals with high level of nasal spike-specific IgA have a lower risk of reinfection. However, mucosal spike-specific sIgA wanes over time, and different individuals may have various level of spike-specific sIgA and descending kinetics, leading to individual differences in susceptibility to reinfection. A method for detecting spike-specific sIgA in the nasal passage would be valuable for predicting the risk of reinfection so that people at risk can have better preparedness.

Methods

In this study, we describe the development of a colloidal gold-based immunochromatographic (ICT) strip for detecting SARS-CoV-2 Omicron spike-specific sIgA in nasal mucosal lining fluids (NMLFs).

Results

The ICT strip was designed to detect 0.125 μg or more spike-specific sIgA in 80 μL of NMLFs collected using a nasal swab. Purified nasal sIgA samples from individuals who recently recovered from an Omicron BA.5 infection were used to demonstrate that this ICT strip can specifically detect spike-specific sIgA. The signal levels positively correlated with neutralizing activities against XBB. Subsequent analysis revealed that people with low or undetectable levels of spike-specific sIgA in the nasal passage were more susceptible to SARS-CoV-2 reinfection.

Conclusions

This nasal spike-specific sIgA ICT strip provides a non-invasive, rapid, and convenient method to assess the risk of reinfection for achieving precision preparedness.

TIGIT+Tfh show poor B-helper function and negatively correlate with SARS-CoV-2 antibody titre

Circulating follicular helper T cells (cTfh) can show phenotypic alterations in disease settings, including in the context of tissue-damaging autoimmune or anti-viral responses. Using severe COVID-19 as a paradigm of immune dysregulation, we have explored how cTfh phenotype relates to the titre and quality of antibody responses. Severe disease was associated with higher titres of neutralising S1 IgG and evidence of increased T cell activation. ICOS, CD38 and HLA-DR expressing cTfh correlated with serum S1 IgG titres and neutralising strength, and interestingly expression of TIGIT by cTfh showed a negative correlation. TIGIT+cTfh expressed increased IFNγ and decreased IL-17 compared to their TIGIT-cTfh counterparts, and showed reduced capacity to help B cells in vitro. Additionally, TIGIT+cTfh expressed lower levels of CD40L than TIGIT-cTfh, providing a potential explanation for their poor B-helper function. These data identify phenotypic changes in polyclonal cTfh that correlate with specific antibody responses and reveal TIGIT as a marker of cTfh with altered function.

PMMA dialyzers modulate both humoral and cell-mediate immune response to anti-COVID-19 vaccine (BNT162b2) in a cohort of chronic hemodialyzed patients

Patients on hemodialysis (HD) have a high risk of death from COVID-19. We evaluated the humoral and cell-mediated immune response to BNT162b2 (Pfizer-BioNTech) vaccine in HD patients, comparing HD with Poly-methyl-methacrylate (PMMA) and HD with Polysulphone (PS). Samples were collected before vaccination (T0) and 14-days after the 2ndvaccine (T2) in a TG (TG, n = 16-Foggia) and in a VG (CG, n = 36-Novara). Anti-SARS-CoV-2-Ig were titrated in the cohort 2-weeks after the 2nddose of vaccine. In the Testing-Group, serum neutralizing antibodies (NAb) were assayed and PBMCs isolated from patients were thawed, counted and stimulated with SARS-CoV-2 IGRA stimulation tube set. All patients had a positive ab-response, except in a case. PMMA-patients had higher levels of anti-SARS-CoV-2 IgG (p = 0.031); VG data confirmed these findings (p < 0.05). NAb evaluation: PMMA patients passed the positive cut-off value, while in PS group only only 1/8 patient did not respond. PMMA patients showed higher percentages of anti-SARS-CoV-2 S1/RBD-Ig after a complete vaccine schedule (p = 0.028). Interferon-gamma release: PMMA patients showed significantly higher release of IFNγ (p = 0.014). The full vaccination course provided sufficient protection against SARS-CoV-2 across the entire cohort, regardless of dialyzer type. After vaccination, PMMA patients show a better immune response, both humoral and cellular, at the end of the vaccination course than PS patients.

Prognostic value of anti-SARS-CoV-2 antibodies: a systematic review

OBJECTIVES

Globally, over 772 million cases of COVID-19 have been reported. New variants of interest with corresponding spikes in case numbers continue to be identified. Vulnerable patients, including older adults or patients with severe comorbidities, continue to be at risk. A large body of evidence has been accumulated regarding anti-SARS-CoV-2-antibodies and COVID-19 but the usefulness of antibody measurements remains unclear. This systematic review aims to assess the prognostic value of anti-SARS-CoV-2-antibodies and their usefulness for guiding booster vaccinations.

METHODS

Studies in English and published between January 2020 and October 2023 were included. Studies that relied on multiparameter-models or comprised fewer than 100 participants were excluded. PubMed and via the WHO COVID-19 research database, Embase and Medline databases were searched. Study selection and quality assessment was conducted independently by two researchers.

RESULTS

After screening 1,160 studies, 33 studies comprising >30 million individuals were included. Anti-SARS-CoV-2-antibodies were strongly associated with reduced risk of SARS-CoV-2-infection and better outcomes, including mortality. Risk of infection and COVID-19 severity decreased with increasing antibody levels.

CONCLUSIONS

Anti-SARS-CoV-2-antibodies are useful for early identification of high-risk patients and timely adjustment of therapy. Protective thresholds may be applied to advise booster vaccinations but verification in separate cohorts is required.

SARS-CoV-2 NSP5 antagonizes MHC II expression by subverting histone deacetylase 2

SARS-CoV-2 interferes with antigen presentation by downregulating major histocompatibility complex (MHC) II on antigen-presenting cells, but the mechanism mediating this process is unelucidated. Herein, analysis of protein and gene expression in human antigen-presenting cells reveals that MHC II is downregulated by the SARS-CoV-2 main protease, NSP5. This suppression of MHC II expression occurs via decreased expression of the MHC II regulatory protein CIITA. CIITA downregulation is independent of the proteolytic activity of NSP5, and rather, NSP5 delivers HDAC2 to the transcription factor IRF3 at an IRF-binding site within the CIITA promoter. Here, HDAC2 deacetylates and inactivates the CIITA promoter. This loss of CIITA expression prevents further expression of MHC II, with this suppression alleviated by ectopic expression of CIITA or knockdown of HDAC2. These results identify a mechanism by which SARS-CoV-2 limits MHC II expression, thereby delaying or weakening the subsequent adaptive immune response.