Assessment of Neutralizing Antibody Response Against SARS-CoV-2 Variants After 2 to 3 Doses of the BNT162b2 mRNA COVID-19 Vaccine

Long-term levels of protection of different types of immunity against the Omicron variant: a rapid literature review

INTRODUCTION

With the emergence of newer SARS-CoV-2 variants and their substantial effects on the levels and duration of protection against infection, an understanding of these characteristics of the protection conferred by humoral and cellular immunity can aid in the proper development and implementation of vaccine and safety guidelines.

METHODS

We conducted a rapid literature review and searched five electronic databases weekly from 1 November 2021 to 30 September 2022. Studies that assessed the humoral or cellular immunity conferred by infection, vaccination or a hybrid (combination of both) in adults and risk groups (immunocompromised and older populations) were identified. Studies were eligible when they reported data on immunological assays of COVID-19 (related to vaccination and/or infection) or the effectiveness of protection (related to the effectiveness of vaccination and/or infection).

RESULTS

We screened 5103 studies and included 205 studies, of which 70 provided data on the duration of protection against SARS-CoV-2 infection. The duration of protection of adaptive immunity was greatly impacted by Omicron and its subvariants: levels of protection were low by 3-6 months from exposure to infection/vaccination. Although more durable, cellular immunity also showed signs of waning by 6 months. First and second mRNA vaccine booster doses increased the levels of protection against infection and severe disease from Omicron and its subvariants but continued to demonstrate a high degree of waning over time.

CONCLUSION

All humoral immunities (infection-acquired, vaccine-acquired and hybrid) waned by 3-6 months. Cellular immunity was more durable but showed signs of waning by 6 months. Hybrid immunity had the highest magnitude of protection against SARS-CoV-2 infection. Boosting may be recommended as early as 3-4 months after the last dose, especially in risk groups.

Second booster dose improves antibody neutralization against BA.1, BA.5 and BQ.1.1 in individuals previously immunized with CoronaVac plus BNT162B2 booster protocol

Introduction

SARS-CoV-2 vaccines production and distribution enabled the return to normalcy worldwide, but it was not fast enough to avoid the emergence of variants capable of evading immune response induced by prior infections and vaccination. This study evaluated, against Omicron sublineages BA.1, BA.5 and BQ.1.1, the antibody response of a cohort vaccinated with a two doses CoronaVac protocol and followed by two heterologous booster doses.

Methods

To assess vaccination effectiveness, serum samples were collected from 160 individuals, in 3 different time points (9, 12 and 18 months after CoronaVac protocol). For each time point, individuals were divided into 3 subgroups, based on the number of additional doses received (No booster, 1 booster and 2 boosters), and a viral microneutralization assay was performed to evaluate neutralization titers and seroconvertion rate.

Results

The findings presented here show that, despite the first booster, at 9m time point, improved neutralization level against omicron ancestor BA.1 (133.1 to 663.3), this trend was significantly lower for BQ.1.1 and BA.5 (132.4 to 199.1, 63.2 to 100.2, respectively). However, at 18m time point, the administration of a second booster dose considerably improved the antibody neutralization, and this was observed not only against BA.1 (2361.5), but also against subvariants BQ.1.1 (726.1) and BA.5 (659.1). Additionally, our data showed that, after first booster, seroconvertion rate for BA.5 decayed over time (93.3% at 12m to 68.4% at 18m), but after the second booster, seroconvertion was completely recovered (95% at 18m).

Discussion

Our study reinforces the concerns about immunity evasion of the SARS-CoV-2 omicron subvariants, where BA.5 and BQ.1.1 were less neutralized by vaccine induced antibodies than BA.1. On the other hand, the administration of a second booster significantly enhanced antibody neutralization capacity against these subvariants. It is likely that, as new SARS-CoV-2 subvariants continue to emerge, additional immunizations will be needed over time.

Immune response to SARS-CoV-2 variants after immunization with different vaccines in Mexico

There is limited information on the antibody responses against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in subjects from developing countries with populations having a high incidence of co-morbidities. Here, we analysed the immunogenicity of homologous schemes using the ChAdOx1-S, Sputnik V, or BNT162b2 vaccines and the effect of a booster dose with ChAdOx1-S in middle-aged adults who were seropositive or seronegative to the SARS-CoV-2 spike protein before vaccination. The study was conducted post-vaccination with a follow-up of 4 months for antibody titre using enzyme-linked immunosorbent assay (ELISA) and pseudovirus (PV) neutralization assays (PNAs). All three vaccines elicited a superior IgG anti-receptor-binding domain (RBD) and neutralization response against the Alpha and Delta variants when administered to individuals with a previous infection by SARS-CoV-2. The booster dose spiked the neutralization activity among individuals with and without a prior SARS-CoV-2 infection. The ChAdOx1-S vaccine induced weaker antibody responses in infection-naive subjects. A follow-up of 4 months post-vaccination showed a drop in antibody titre, with about 20% of the infection-naive and 100% of SARS-CoV-2 pre-exposed participants with detectable neutralization capacity against Alpha pseudovirus (Alpha-PV) and Delta PV (Delta-PV). Our observations support the use of different vaccines in a country with high seroprevalence at the vaccination time.

Humoral and cellular immune response in patients of liver cirrhosis and immunocompetent recipient of ChAdOx1nCoV-19 Vaccine (Covishield)

Despite the effectiveness of COVID-19 vaccination in reducing the severity of the disease, the demand for booster is increasing in vulnerable populations like elderly and immunocompromised individuals especially with each new wave of COVID-19 in different countries. There is limited data on the sustained immunity against COVID-19 in patients with liver cirrhosis. The study was aimed to compare the T cell and humoral immune response after 1 year of ChAdOx1nCoV-19 Vaccine in patients with liver cirrhosis and healthy health care workers (HCW). This was a prospective observational study including 36 HCW, 19 liver cirrhosis patients and 10 unvaccinated individuals. Anti-SARS-CoV-2S antibody, neutralizing antibody and memory T cell subsets were evaluated by ELISA and flow cytometry, respectively, in all three groups after 1 year of initial vaccination. Compared to HCW and unvaccinated individuals, liver cirrhosis patients had significantly depleted T cells, although CD4:CD8 + T cell ratio was normal. Both cirrhotic patients and HCW developed memory T cell subset [effector memory RA (P = 0.141, P < 0.001), effector memory (P < 0.001, P < 0.001), central memory (P < 0.001, P < 0.01), stem cell memory (P = 0.009, P = 0.08) and naïve (P < 0.001, P = 0.02)] compared to unvaccinated unexposed individuals of CD4 + T and CD8 + T, respectively. However, among HCW and cirrhotic group no difference was noted on central memory and stem cell memory cells on T cells. Patients with liver cirrhosis developed comparable memory T cells after vaccination which can evoke sustainable immune response on reinfection. Therefore, additional vaccine doses may not be necessary for cirrhosis patients.

Dynamics of humoral and cellular response to three doses of anti-SARS-CoV-2 BNT162b2 vaccine in patients with hematological malignancies and older subjects

Background

Few data are available about the durability of the response, the induction of neutralizing antibodies, and the cellular response upon the third dose of the anti-severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccine in hemato-oncological patients.

Objective

To investigate the antibody and cellular response to the BNT162b2 vaccine in patients with hematological malignancy.

Methods

We measured SARS-CoV-2 anti-spike antibodies, anti-Omicron neutralizing antibodies, and T-cell responses 1 month after the third dose of vaccine in 93 fragile patients with hematological malignancy (FHM), 51 fragile not oncological subjects (FNO) aged 80-92, and 47 employees of the hospital (healthcare workers, (HW), aged 23-66 years. Blood samples were collected at day 0 (T0), 21 (T1), 35 (T2), 84 (T3), 168 (T4), 351 (T pre-3D), and 381 (T post-3D) after the first dose of vaccine. Serum IgG antibodies against S1/S2 antigens of SARS-CoV-2 spike protein were measured at every time point. Neutralizing antibodies were measured at T2, T3 (anti-Alpha), T4 (anti-Delta), and T post-3D (anti-Omicron). T cell response was assessed at T post-3D.

Results

An increase in anti-S1/S2 antigen antibodies compared to T0 was observed in the three groups at T post-3D. After the third vaccine dose, the median antibody level of FHM subjects was higher than after the second dose and above the putative protection threshold, although lower than in the other groups. The neutralizing activity of antibodies against the Omicron variant of the virus was tested at T2 and T post-3D. 42.3% of FHM, 80,0% of FNO, and 90,0% of HW had anti-Omicron neutralizing antibodies at T post-3D. To get more insight into the breadth of antibody responses, we analyzed neutralizing capacity against BA.4/BA.5, BF.7, BQ.1, XBB.1.5 since also for the Omicron variants, different mutations have been reported especially for the spike protein. The memory T-cell response was lower in FHM than in FNO and HW cohorts. Data on breakthrough infections and deaths suggested that the positivity threshold of the test is protective after the third dose of the vaccine in all cohorts.

Conclusion

FHM have a relevant response to the BNT162b2 vaccine, with increasing antibody levels after the third dose coupled with, although low, a T-cell response. FHM need repeated vaccine doses to attain a protective immunological response.

Clinical and laboratory considerations: determining an antibody-based composite correlate of risk for reinfection with SARS-CoV-2 or severe COVID-19

Much of the global population now has some level of adaptive immunity to SARS-CoV-2 induced by exposure to the virus (natural infection), vaccination, or a combination of both (hybrid immunity). Key questions that subsequently arise relate to the duration and the level of protection an individual might expect based on their infection and vaccination history. A multi-component composite correlate of risk (CoR) could inform individuals and stakeholders about protection and aid decision making. This perspective evaluates the various elements that need to be accommodated in the development of an antibody-based composite CoR for reinfection with SARS-CoV-2 or development of severe COVID-19, including variation in exposure dose, transmission route, viral genetic variation, patient factors, and vaccination status. We provide an overview of antibody dynamics to aid exploration of the specifics of SARS-CoV-2 antibody testing. We further discuss anti-SARS-CoV-2 immunoassays, sample matrices, testing formats, frequency of sampling and the optimal time point for such sampling. While the development of a composite CoR is challenging, we provide our recommendations for each of these key areas and highlight areas that require further work to be undertaken.

Impact of methotrexate on humoral and cellular immune responses to SARS-CoV-2 mRNA vaccine in patients with rheumatoid arthritis

The aim of this study was to longitudinally evaluate the undetermined impact of methotrexate (MTX) on the cumulative immunogenicity elicited by three doses of SARS-CoV-2 mRNA vaccination in patients with rheumatoid arthritis (RA). We prospectively evaluated vaccine-induced immune responses following the first dose, 1 and 6 months after the second dose, and 1 month after the third dose of BNT162b2 or mRNA-1273 in 144 SARS-CoV-2 naïve participants (70 patients with RA, 29 disease controls without immunosuppressive conditions, and 45 healthy controls). Humoral immune responses were assessed by quantifying anti-spike IgG antibody titers and the capacity of circulating antibodies to neutralize the ancestral SARS-CoV-2 strain and the Alpha, Delta, and Omicron variants. Vaccine-induced T-cell responses were measured using an interferon-gamma release assay. At 1 and 6 months after the second dose, anti-spike titers were highest in healthy controls, followed by disease controls and patients with RA. Multivariate analyses revealed that MTX treatment was significantly associated with a decrease in anti-spike titers, neutralizing activity, and SARS-CoV-2-specific interferon-gamma levels. Furthermore, MTX dose per body weight was negatively correlated with these two indices of humoral immune response. The third vaccine dose boosted anti-spike titers, especially in patients receiving MTX, while sera from these patients neutralized the Omicron variant far less robustly than those from healthy controls. In conclusion, MTX attenuated immunogenicity following two doses of SARS-CoV-2 mRNA vaccine in patients with RA, particularly resulting in dose-dependent suppression of the humoral immune response. Furthermore, MTX deteriorated the neutralizing activity against the Omicron variant, even after the third immunization.

Safety and Immunogenicity of SARS-CoV-2 Recombinant Spike Protein Vaccine in Children and Adolescents in India: A Phase 2-3 Randomized Clinical Trial

Importance

The recombinant COVID-19 vaccine NVX-CoV2373 has demonstrated efficacy of approximately 90% in adults; however, its safety and efficacy in children is unknown.

Objective

To assess the noninferiority of SII-NVX-CoV2373 in children and adolescents compared to adults and to evaluate its safety in comparison with placebo.

Design, Setting, and Participants

This phase 2-3 observer-blind randomized clinical trial was conducted in 2 cohorts, children (aged 2 to 11 years) and adolescents (aged 12 to 17 years) between August 2021 and August 2022. Participants were randomized 3:1 to SII-NVX-CoV2373 or placebo and monitored for 179 days. The participants, study team, and laboratory staff were blinded. This was a multicenter study conducted across 10 tertiary care hospitals in India. Exclusion criteria included previous COVID-19 infection or vaccination, immunocompromised condition, and immunosuppressive medications.

Interventions

Two doses of 0.5-mL SII-NVX-CoV2373 or placebo were administered intramuscularly on days 1 and 22.

Main Outcomes and Measures

Primary outcomes were geometric mean titer ratio of both anti-spike (anti-S) IgG and neutralizing antibodies (NAbs) between both pediatric age groups to that of adults on day 36. Noninferiority was concluded if the lower bound of 95% CI of this ratio was greater than 0.67 for each age group. Both the antibodies were assessed for the index strain and for selected variants at various time points. Solicited adverse events (AEs) were recorded for 7 days after each vaccination, unsolicited AEs were recorded for 35 days, and serious AEs and AEs of special interest were recorded for 179 days.

Results

A total of 460 children in each age cohort were randomized to receive vaccine or placebo. The mean (SD) age was 6.7 (2.7) years in the child cohort and 14.3 (1.6) years in the adolescent cohort; 231 participants (50.2%) in the child cohort and 218 in the adolescent cohort (47.4%) were female. Both anti-S IgG and NAb titers were markedly higher in the SII-NVX-CoV2373 group than in the placebo group on both day 36 and day 180. The geometric mean titer ratios compared to those in adults were 1.20 (95% CI, 1.08-1.34) and 1.52 (95% CI, 1.38-1.67) for anti-S IgG in adolescents and children, respectively; while for NAbs, they were 1.33 (95% CI, 1.17-1.50) and 1.93 (95% CI, 1.70-2.18) in adolescents and children, respectively, indicating noninferiority. SII-NVX-CoV2373 also showed immune responses against variants studied. Injection site reactions, fever, headache, malaise, and fatigue were common solicited AEs. There were no AEs of special interest and no causally related serious AEs.

Conclusions and Relevance

SII-NVX-CoV2373 was safe and well tolerated in children and adolescents in this study. The vaccine was highly immunogenic and may be used in pediatric vaccination against COVID-19.

Trial Registration

Clinical Trials Registry of India Identifier: CTRI/2021/02/031554.

Identification and Analysis of Monoclonal Antibodies with Neutralizing Activity against Diverse SARS-CoV-2 Variants

We identified neutralizing monoclonal antibodies against severe acute respiratory syndrome-coronavirus 2 (SARS-CoV-2) variants (including Omicron variants BA.5 and BA.2.75) from individuals who received two doses of mRNA vaccination after they had been infected with the D614G virus. We named them MO1, MO2, and MO3. Among them, MO1 showed particularly high neutralizing activity against authentic variants: D614G, Delta, BA.1, BA.1.1, BA.2, BA.2.75, and BA.5. Furthermore, MO1 suppressed BA.5 infection in hamsters. A structural analysis revealed that MO1 binds to the conserved epitope of seven variants, including Omicron variants BA.5 and BA.2.75, in the receptor-binding domain of the spike protein. MO1 targets an epitope conserved among Omicron variants BA.1, BA.2, and BA.5 in a unique binding mode. Our findings confirm that D614G-derived vaccination can induce neutralizing antibodies that recognize the epitopes conserved among the SARS-CoV-2 variants. IMPORTANCE Omicron variants of SARS-CoV-2 acquired escape ability from host immunity and authorized antibody therapeutics and thereby have been spreading worldwide. We reported that patients infected with an early SARS-CoV-2 variant, D614G, and who received subsequent two-dose mRNA vaccination have high neutralizing antibody titer against Omicron lineages. It was speculated that the patients have neutralizing antibodies broadly effective against SARS-CoV-2 variants by targeting common epitopes. Here, we explored human monoclonal antibodies from B cells of the patients. One of the monoclonal antibodies, named MO1, showed high potency against broad SARS-CoV-2 variants including BA.2.75 and BA.5 variants. The results prove that monoclonal antibodies that have common neutralizing epitopes among several Omicrons were produced in patients infected with D614G and who received mRNA vaccination.

COVID-19 vaccine effectiveness against symptomatic infection and hospitalisation in Belgium, July 2021 to May 2022

BackgroundThe Belgian COVID-19 vaccination campaign aimed to reduce disease spread and severity.AimWe estimated SARS-CoV-2 variant-specific vaccine effectiveness against symptomatic infection (VEi) and hospitalisation (VEh), given time since vaccination and prior infection.MethodsNationwide healthcare records from July 2021 to May 2022 on testing and vaccination were combined with a clinical hospital survey. We used a test-negative design and proportional hazard regression to estimate VEi and VEh, controlling for prior infection, time since vaccination, age, sex, residence and calendar week of sampling.ResultsWe included 1,932,546 symptomatic individuals, of whom 734,115 tested positive. VEi against Delta waned from an initial estimate of 80% (95% confidence interval (CI): 80-81) to 55% (95% CI: 54-55) 100-150 days after the primary vaccination course. Booster vaccination increased initial VEi to 85% (95% CI: 84-85). Against Omicron, an initial VEi of 33% (95% CI: 30-36) waned to 17% (95% CI: 15-18), while booster vaccination increased VEi to 50% (95% CI: 49-50), which waned to 20% (95% CI: 19-21) 100-150 days after vaccination. Initial VEh for booster vaccination decreased from 96% (95% CI: 95-96) against Delta to 87% (95% CI: 86-89) against Omicron. VEh against Omicron waned to 73% (95% CI: 71-75) 100-150 days after booster vaccination. While recent prior infections conferred higher protection, infections occurring before 2021 remained associated with significant risk reduction against symptomatic infection. Vaccination and prior infection outperformed vaccination or prior infection only.ConclusionWe report waning and a significant decrease in VEi and VEh from Delta to Omicron-dominant periods. Booster vaccination and prior infection attenuated these effects.

Fourth mRNA vaccination increases cross-neutralizing antibody titers against SARS-CoV-2 variants, including BQ.1.1 and XBB, in a very elderly population

BACKGROUND

Omicron variants with immune evasion have emerged, and they continue to mutate rapidly, raising concerns about the weakening of vaccine efficacy, and the very elderly populations are vulnerable to Coronavirus Disease 2019 (COVID-19). Therefore, to investigate the effect of multiple doses of mRNA vaccine for the newly emerged variants on these populations, cross-neutralizing antibody titers were examined against Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) variants, including BQ.1.1 and XBB.

METHODS

Blood samples were taken from residents at four long-term care facilities in Hyogo prefecture, Japan (median age, 91 years), after 3rd (n = 67) and 4th (n = 48) mRNA vaccinations, from April to October 2022. A live virus microneutralization assay was performed to determine the neutralizing antibody titers in participants' sera.

RESULTS

After 3rd vaccination, cross-neutralizing antibody prevalence against conventional (D614G) virus, Delta, Omicron BA.2, BA.5, BA.2.75, BQ.1.1, and XBB were 100%, 97%, 81%, 51%, 67%, 4%, and 21%, respectively. After 4th vaccination, the antibody positivity rates increased to 100%, 100%, 98%, 79%, 92%, 31%, and 52%, respectively. The 4th vaccination significantly increased cross-neutralizing antibody titers against all tested variants.

CONCLUSION

The positivity rates for BQ.1.1 and XBB increased after 4th vaccination, although the titer value was lower than those of BA.5 and BA.2.75. Considering the rapid mutation of viruses and the efficacy of vaccines, it may be necessary to create a system that can develop vaccines suitable for each epidemic in consideration of the epidemic of the virus.

Adenosine deaminase augments SARS-CoV-2 specific cellular and humoral responses in aged mouse models of immunization and challenge

Despite numerous clinically available vaccines and therapeutics, aged patients remain at increased risk for COVID-19 morbidity. Furthermore, various patient populations, including the aged can have suboptimal responses to SARS-CoV-2 vaccine antigens. Here, we characterized vaccine-induced responses to SARS-CoV-2 synthetic DNA vaccine antigens in aged mice. Aged mice exhibited altered cellular responses, including decreased IFNγ secretion and increased TNFα and IL-4 secretion suggestive of TH2-skewed responses. Aged mice exhibited decreased total binding and neutralizing antibodies in their serum but significantly increased TH2-type antigen-specific IgG1 antibody compared to their young counterparts. Strategies to enhance vaccine-induced immune responses are important, especially in aged patient populations. We observed that co-immunization with plasmid-encoded adenosine deaminase (pADA)enhanced immune responses in young animals. Ageing is associated with decreases in ADA function and expression. Here, we report that co-immunization with pADA enhanced IFNγ secretion while decreasing TNFα and IL-4 secretion. pADA expanded the breadth and affinity SARS-CoV-2 spike-specific antibodies while supporting TH1-type humoral responses in aged mice. scRNAseq analysis of aged lymph nodes revealed that pADA co-immunization supported a TH1 gene profile and decreased FoxP3 gene expression. Upon challenge, pADA co-immunization decreased viral loads in aged mice. These data support the use of mice as a model for age-associated decreased vaccine immunogenicity and infection-mediated morbidity and mortality in the context of SARS-CoV-2 vaccines and provide support for the use of adenosine deaminase as a molecular adjuvant in immune-challenged populations.

Antibody response to third and fourth BNT162b2 mRNA booster vaccinations in healthcare workers in Tokyo, Japan

BACKGROUND

Booster vaccinations against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are being promoted worldwide to counter the coronavirus disease 2019 (COVID-19) pandemic. In this study, we analyzed the longitudinal effect of the third BNT162b2 mRNA vaccination on antibody responses in healthcare workers. Additionally, antibody responses induced by the fourth vaccination were analyzed.

METHODS

The levels of anti-spike (S) IgG and neutralizing antibody against SARS-CoV-2 were measured at 7 months after the second vaccination (n = 1138), and at 4 (n = 701) and 7 (n = 417) months after the third vaccination using an iFlash 3000 chemiluminescence immunoassay analyzer. Among the 417 participants surveyed at 7 months after the third vaccination, 40 had received the fourth vaccination. A multiple linear regression analysis was performed to clarify which factors were associated with the anti-S IgG and neutralizing antibody. Variables assessed included sex, age, number of days after the second or third vaccination, diagnostic history of COVID-19, and anti-nucleocapsid (N) IgG level.

RESULTS

At 7 months after the third vaccination, antibody responses were significantly higher than those at the same time after the second vaccination. Unlike the second vaccination, age had no effect on the antibody responses induced by the third vaccination. Furthermore, the fourth vaccination resulted in a further increase in antibody responses. The multiple linear regression analysis identified anti-N IgG level, presumably associated with infection, as a factor associated with antibody responses.

CONCLUSIONS

Our findings showed that BNT162b2 booster vaccinations increased and sustained the antibody responses against SARS-CoV-2.

Neutralization of Omicron subvariants BA.1 and BA.5 by a booster dose of COVID-19 mRNA vaccine in a Japanese nursing home cohort

The sustained epidemic of Omicron subvariants of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a worldwide concern, and older adults are at high risk. We conducted a prospective cohort study to assess the immunogenicity of COVID-19 mRNA vaccines (BNT162b2 or mRNA-1273) in nursing home residents and staff between May 2021 and December 2022. A total of 335 SARS-CoV-2 naïve individuals, including 141 residents (median age: 88 years) and 194 staff (median age: 44 years) participated. Receptor-binding domain (RBD) and nucleocapsid (N) protein IgG and neutralizing titer (NT) against the Wuhan strain, Alpha and Delta variants, and Omicron BA.1 and BA.5 subvariants were measured in serum samples drawn from participants after the second and third doses of mRNA vaccine using SARS-CoV-2 pseudotyped virus. Breakthrough infection (BTI) was confirmed by a notification of COVID-19 or a positive anti-N IgG result in serum after mRNA vaccination. Fifty-one participants experienced SARS-CoV-2 BTI during the study period. The RBD IgG and NTs against Omicron BA.1 and BA.5 were markedly increased in SARS CoV-2 naïve participants 2 months after the third dose of mRNA vaccine, compared to those 5 months after the second dose, and declined 5 months after the third dose. The decline in RBD IgG and NT against Omicron BA.1 and BA.5 in SARS-CoV-2 naïve participants after the second and the third dose was particularly marked in those aged ≥ 80 years. BTIs during the BA.5 epidemic period, which occurred between 2 and 5 months after the third dose, induced a robust NT against BA.5 even five months after the booster dose vaccination. Further studies are required to assess the sustainability of NTs elicited by Omicron-containing bivalent mRNA booster vaccine in older adults.

Clinical usefulness of testing for severe acute respiratory syndrome coronavirus 2 antibodies

In the COVID-19 pandemic era, antibody testing against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has proven an invaluable tool and herein we highlight some of the most useful clinical and/or epidemiological applications of humoral immune responses recording. Anti-spike circulating IgGs and SARS-CoV-2 neutralizing antibodies can serve as predictors of disease progression or disease prevention, whereas anti-nucleocapsid antibodies can help distinguishing infection from vaccination. Also, in the era of immunotherapies we address the validity of anti-SARS-CoV-2 antibody monitoring post-infection and/or vaccination following therapies with the popular anti-CD20 monoclonals, as well as in the context of various cancers or autoimmune conditions such as rheumatoid arthritis and multiple sclerosis. Additional crucial applications include population immunosurveillance, either at the general population or at specific communities such as health workers. Finally, we discuss how testing of antibodies in cerebrospinal fluid can inform us on the neurological complications that often accompany COVID-19.

Long-term adaptive response in COVID-19 vaccine recipients and the effect of a booster dose

We examined the immune response in subjects previously infected with SARS-CoV2 and infection-naïve 9 months after primary 2-dose COVID-19 mRNA vaccination and 3 months after the booster dose in a longitudinal cohort of healthcare workers. Nine months after primary vaccination, previously infected subjects exhibited higher residual antibody levels, with significant neutralizing activity against distinct variants compared to infection-naïve subjects. The higher humoral response was associated with higher levels of receptor binding domain (RBD)-specific IgG⁺ and IgA⁺ memory B cells. The booster dose increased neither neutralizing activity, nor the B and T cell frequencies. Conversely, infection-naïve subjects needed the booster to achieve comparable levels of neutralizing antibodies as those found in previously infected subjects after primary vaccination. The neutralizing titer correlated with anti-RBD IFNγ producing T cells, in the face of sustained B cell response. Notably, pre-pandemic samples showed high Omicron cross-reactivity. These data show the importance of the booster dose in reinforcing immunological memory and increasing circulating antibodies in infection-naïve subjects.

Evaluation of antibody response to SARS-CoV-2 variants after 2 doses of mRNA COVID-19 vaccine in a correctional facility

The SARS-CoV-2 pandemic has posed a challenge for correctional facilities worldwide. People in such settings are more vulnerable to severe forms of infection and it is impossible to completely isolate inmates from the outside world. This study aimed to assess the antibody-mediated immune response in terms of neutralizing antibodies against Alpha, Beta, Gamma and Omicron (sub-lineage BA.1) variants of concern after two doses of mRNA vaccine in correctional officers and inmates from an Italian correctional facility. Most of the correctional officers (56.5%) and inmates (52.3% and 63.6%) retained their neutralizing activity toward the Alpha and Gamma variants, respectively. By contrast, the most striking reduction in comparison with the ancestral virus was found in the antibody response toward the Beta and Omicron variants, in both correctional officers (91.2% and 93.9%) and inmates (85.1% and 92.8%). In addition, subjects who had undergone primary vaccination and had previously been naturally infected had higher neutralizing antibody titers toward the 4 variants than negative subjects. Overall, our findings indicate that primary mRNA vaccination is able to induce neutralizing antibodies toward the ancestral virus, while titers toward variants may vary, depending on the mutations harboring by the variants. Although the correctional setting is often considered distinct or isolated from the wider society and sanitary system, the health of correctional workers and prisoners is inexorably linked to the public health of the country as a whole and it is of paramount importance to monitor the antibody response in these settings.

Humoral immunity and B-cell memory in response to SARS-CoV-2 infection and vaccination

Natural infection with SARS-CoV-2 induces a robust circulating memory B cell (Bmem) population, which remains stable in number at least 8 months post-infection despite the contraction of antibody levels after 1 month. Multiple vaccines have been developed to combat the virus. These include two new formulations, mRNA and adenoviral vector vaccines, which have varying efficacy rates, potentially related to their distinct capacities to induce humoral immune responses. The mRNA vaccines BNT162b2 (Pfizer-BioNTech) and mRNA-1273 (Moderna) elicit significantly higher serum IgG and neutralizing antibody levels than the adenoviral vector ChAdOx1 (AstraZeneca) and Ad26.COV2.S (Janssen) vaccines. However, all vaccines induce Spike- and RBD-specific Bmem, which are vital in providing long-lasting protection in the form of rapid recall responses to subsequent infections. Past and current SARS-CoV-2 variants of concern (VoC) have shown the capacity to escape antibody neutralization to varying degrees. A booster dose with an mRNA vaccine following primary vaccination restores antibody levels and improves the capacity of these antibodies and Bmem to bind viral variants, including the current VoC Omicron. Future experimental research will be essential to evaluate the durability of protection against VoC provided by each vaccine and to identify immune markers of protection to enable prognostication of people who are at risk of severe complications from COVID-19.

Real-World Effectiveness of a Booster Dose of the COVID-19 Vaccines among Japanese University Students

With the spread of the Coronavirus disease 2019 (COVID-19), missing learning opportunities due to COVID-19 has been raised as a major concern for university education. We aimed to examine the effectiveness of a booster dose of COVID-19 vaccines among Japanese university students during the spread of the Omicron variant. We enrolled 249 students who became a close contact and 294 COVID-19-infected students though the Hiroshima University COVID-19 registration system. Infection rates of people in close contact with sick individuals and symptoms of infected students were examined. Close contacts who had received a booster dose showed a significantly lower infection rate (31%) compared with those with two doses (50%, p = 0.02) and the unvaccinated (71%, p = 0.002). Age- and sex-adjusted odds ratios of receipt of a booster dose vs. two doses and unvaccinated were 0.40 (95% confidence interval [CI], 0.23−0.70, p = 0.001) and 0.44 (95% CI, 0.25−0.77, p = 0.004), respectively. The incidence of severe fever (38.5°C or higher) was significantly less prevalent in those with a booster dose (16%) compared with two doses (40%, p = 0.002) and those who were unvaccinated (75%, p < 0.0001). Booster doses reduced infection rates among close-contact students and can help students to avoid missing learning opportunities.

Cross-reactivity of eight SARS-CoV-2 variants rationally predicts immunogenicity clustering in sarbecoviruses

A steep rise in Omicron reinfection cases suggests that this variant has increased immune evasion ability. To evaluate its antigenicity relationship with other variants, antisera from guinea pigs immunized with spike protein of SARS-CoV-2 variants of concern (VOCs) and variants of interest (VOIs) were cross-tested against pseudotyped variants. The neutralization activity against Omicron was markedly reduced when other VOCs or VOIs were used as immunogens, and Omicron (BA.1)-elicited sera did not efficiently neutralize the other variants. However, a Beta or Omicron booster, when administered as the 4th dose 3-months after the 3rd dose of any of the variants, could elicit broad neutralizing antibodies against all of the current variants including Omicron BA.1. Further analysis with 280 available antigen-antibody structures and quantification of immune escape from 715 reported neutralizing antibodies provide explanations for the observed differential immunogenicity. Three distinct clades predicted using an in silico algorithm for clustering of sarbecoviruses based on immune escape provide key information for rational design of vaccines.

Increased Secondary Attack Rates among the Household Contacts of Patients with the Omicron Variant of the Coronavirus Disease 2019 in Japan

This study investigated the household secondary attack rate (HSAR) of patients with coronavirus disease (COVID-19) during the omicron variant-dominant period. The HSAR of COVID-19 cases during the omicron variant-dominant period (4–20 January 2022) was calculated and compared with the delta variant-dominant period (20 August to 7 November 2021) in Itako, Japan. In Itako, all 47 and 119 samples tested during the omicron and delta variant-dominant periods were negative and positive, respectively, for the L452R mutation. We used a generalized estimating equation regression model. The HSAR was 31.8% (95% confidence interval (CI) 27.7–36.2) for 456 household contacts during the omicron variant-dominant period; it was higher than that during the delta variant-dominant period (25.2%) (adjusted risk ratio [aRR] 1.61, CI 1.13–2.28). During the omicron variant-dominant period, HSAR was lower for the household contacts of completely vaccinated index patients (27.3%) than for contacts of other index patients (41.2%) (vaccine effectiveness for infectee 0.43, 95% CI 0.16–0.62) and was significantly higher for female contacts than for male contacts (36.2% vs. 26.1%; aRR 1.29, 95% CI 1.01–1.65). The HSAR was significantly higher during the omicron variant-dominant period than the delta variant-dominant period. The vaccination of index patients might protect household contacts.

Individuals With Weaker Antibody Responses After Booster Immunization Are Prone to Omicron Breakthrough Infections

Background

Despite the high level of protection against severe COVID-19 provided by the currently available vaccines some breakthrough infections occur. Until now, there is no information whether a potential risk of a breakthrough infection can be inferred from the level of antibodies after booster vaccination.

Methods

Levels of binding antibodies and neutralization capacity after the first, one and six month after the second, and one month after the third (booster) vaccination against COVID-19 were measured in serum samples from 1391 healthcare workers at the University Hospital Essen. Demographics, vaccination scheme, pre-infection antibody titers and neutralization capacity were compared between individuals with and without breakthrough infections.

Results

The risk of developing an Omicron breakthrough infection was independent of vaccination scheme, sex, body mass index, smoking status or pre-existing conditions. In participants with low pre-infection anti-spike antibodies (≤ 2641.0 BAU/ml) and weaker neutralization capacity (≤ 65.9%) against Omicron one month after the booster vaccination the risk for developing an Omicron infection was 10-fold increased (P = 0.001; 95% confidence interval, 2.36 - 47.55).

Conclusion

Routine testing of anti-SARS-CoV-2 IgG antibodies and surrogate virus neutralization can quantify vaccine-induced humoral immune response and may help to identify subjects who are at risk for a breakthrough infection. The establishment of thresholds for SARS-CoV-2 IgG antibody levels identifying “non”-, “low” and “high”-responders may be used as an indication for re-vaccination.