Decreased memory B cell frequencies in COVID-19 delta variant vaccine breakthrough infection

Robust and persistent B-cell responses following SARS-CoV-2 vaccine determine protection from SARS-CoV-2 infection

Introduction

A clear immune correlate of protection from severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection has not been defined. We explored antibody, B-cell, and T-cell responses to the third-dose vaccine and relationship to incident SARS-CoV-2 infection.

Methods

Adults in a prospective cohort provided blood samples at day 0, day 14, and 10 months after the third-dose SARS-CoV-2 vaccine. Participants self-reported incident SARS-CoV-2 infection. Plasma anti-SARS-CoV-2 receptor-binding domain (RBD) and spike-subunit-1 and spike-subunit-2 antibodies were measured. A sub-study assessed SARS-CoV-2-specific plasma and memory B-cell and memory T-cell responses in peripheral blood mononuclear cells by enzyme-linked immunospot. Comparative analysis between participants who developed incident infection and uninfected participants utilised non-parametric t-tests, Kaplan-Meier survival analysis, and Cox proportional hazard ratios.

Results

Of the 132 participants, 47 (36%) reported incident SARS-CoV-2 infection at a median 16.5 (16.25-21) weeks after the third-dose vaccination. RBD titres and B-cell responses, but not T-cell responses, increased after the third-dose vaccine. Whereas no significant difference in day 14 antibody titres or T-cell responses was observed between participants with and without incident SARS-CoV-2 infection, RBD memory B-cell frequencies were significantly higher in those who did not develop infection [10.0% (4.5%-16.0%) versus 4.9% (1.6%-9.3%), p = 0.01]. RBD titres and memory B-cell frequencies remained significantly higher at 10 months than day 0 levels (p < 0.01).

Discussion

Robust antibody and B-cell responses persisted at 10 months following the third-dose vaccination. Higher memory B-cell frequencies, rather than antibody titres or T-cell responses, predicted protection from subsequent infection, identifying memory B cells as a correlate of protection.

Modeling and predicting individual variation in COVID-19 vaccine-elicited antibody response in the general population

As we learned during the COVID-19 pandemic, vaccines are one of the most important tools in infectious disease control. To date, an unprecedentedly large volume of high-quality data on COVID-19 vaccinations have been accumulated. For preparedness in future pandemics beyond COVID-19, these valuable datasets should be analyzed to best shape an effective vaccination strategy. We are collecting longitudinal data from a community-based cohort in Fukushima, Japan, that consists of 2,407 individuals who underwent serum sampling two or three times after a two-dose vaccination with either BNT162b2 or mRNA-1273. Using the individually reconstructed time courses of the vaccine-elicited antibody response based on mathematical modeling, we first identified basic demographic and health information that contributed to the main features of the antibody dynamics, i.e., the peak, the duration, and the area under the curve. We showed that these three features of antibody dynamics were partially explained by underlying medical conditions, adverse reactions to vaccinations, and medications, consistent with the findings of previous studies. We then applied to these factors a recently proposed computational method to optimally fit an "antibody score", which resulted in an integer-based score that can be used as a basis for identifying individuals with higher or lower antibody titers from basic demographic and health information. The score can be easily calculated by individuals themselves or by medical practitioners. Although the sensitivity of this score is currently not very high, in the future, as more data become available, it has the potential to identify vulnerable populations and encourage them to get booster vaccinations. Our mathematical model can be extended to any kind of vaccination and therefore can form a basis for policy decisions regarding the distribution of booster vaccines to strengthen immunity in future pandemics.

To be remembered: B cell memory response against SARS-CoV-2 and its variants in vaccinated and unvaccinated individuals

COVID-19 disease has plagued the world economy and affected the overall well-being and life of most of the people. Natural infection as well as vaccination leads to the development of an immune response against the pathogen. This involves the production of antibodies, which can neutralize the virus during future challenges. In addition, the development of cellular immune memory with memory B and T cells provides long-lasting protection. The longevity of the immune response has been a subject of intensive research in this field. The extent of immunity conferred by different forms of vaccination or natural infections remained debatable for long. Hence, understanding the effectiveness of these responses among different groups of people can assist government organizations in making informed policy decisions. In this article, based on the publicly available data, we have reviewed the memory response generated by some of the vaccines against SARS-CoV-2 and its variants, particularly B cell memory in different groups of individuals.

Suppressed transcript diversity and immune response in COVID-19 ICU patients: a longitudinal study

Understanding the dynamic changes in gene expression during Acute Respiratory Distress Syndrome (ARDS) progression in post-acute infection patients is crucial for unraveling the underlying mechanisms. Study investigates the longitudinal changes in gene/transcript expression patterns in hospital-admitted severe COVID-19 patients with ARDS post-acute SARS-CoV-2 infection. Blood samples were collected at three time points and patients were stratified into severe and mild ARDS, based on their oxygenation saturation (SpO2/FiO2) kinetics over 7 d. Decline in transcript diversity was observed over time, particularly in patients with higher severity, indicating dysregulated transcriptional landscape. Comparing gene/transcript-level analyses highlighted a rather limited overlap. With disease progression, a transition towards an inflammatory state was evident. Strong association was found between antibody response and disease severity, characterized by decreased antibody response and activated B cell population in severe cases. Bayesian network analysis identified various factors associated with disease progression and severity, viz. humoral response, TLR signaling, inflammatory response, interferon response, and effector T cell abundance. The findings highlight dynamic gene/transcript expression changes during ARDS progression, impact on tissue oxygenation and elucidate disease pathogenesis.

Elevated BMI reduces the humoral response to SARS-CoV-2 infection

Objective

Class III obesity (body mass index [BMI] ≥ 40 kg m-2) significantly impairs the immune response to SARS-CoV-2 vaccination. However, the effect of an elevated BMI (≥ 25 kg m-2) on humoral immunity to SARS-CoV-2 infection and COVID-19 vaccination remains unclear.

Methods

We collected blood samples from people who recovered from SARS-CoV-2 infection approximately 3 and 13 months of post-infection (noting that these individuals were not exposed to SARS-CoV-2 or vaccinated in the interim). We also collected blood samples from people approximately 5 months of post-second dose COVID-19 vaccination (the majority of whom did not have a prior SARS-CoV-2 infection). We measured their humoral responses to SARS-CoV-2, grouping individuals based on a BMI greater or less than 25 kg m-2.

Results

Here, we show that an increased BMI (≥ 25 kg m-2), when accounting for age and sex differences, is associated with reduced antibody responses after SARS-CoV-2 infection. At 3 months of post-infection, an elevated BMI was associated with reduced antibody titres. At 13 months of post-infection, an elevated BMI was associated with reduced antibody avidity and a reduced percentage of spike-positive B cells. In contrast, no significant association was noted between a BMI ≥ 25 kg m-2 and humoral immunity to SARS-CoV-2 at 5 months of post-secondary vaccination.

Conclusions

Taken together, these data showed that elevated BMI is associated with an impaired humoral immune response to SARS-CoV-2 infection. The impairment of infection-induced immunity in individuals with a BMI ≥ 25 kg m-2 suggests an added impetus for vaccination rather than relying on infection-induced immunity.

Higher Delta variant-specific neutralizing antibodies prevented infection in close contacts vaccinated with ancestral mRNA vaccines during the SARS-CoV-2 Delta wave

Identification of the risk factors and the high-risk groups which are most vulnerable is critical in COVID-19 disease management at a population level. Evaluating the efficacy of vaccination against infections is necessary to determine booster vaccination strategies for better protection in high-risk groups. In this study, we recruited 158 mRNA-vaccinated individuals during the Delta wave of SARS-CoV-2 infections in Singapore and examined the antibody profiles of infected individuals. We found that, despite high exposure due to communal living conditions in proximity, 4% of individuals (6/158) had PCR-confirmed infections and 96% (152/158) remained uninfected. Time-course analysis of the antibody profile at the start and the end of quarantine period showed Delta-specific boosting of anti-spike antibody response in 57% of the uninfected individuals (86/152). In the remaining 43% of the uninfected individuals (66/152) with no Delta-specific antibody boost, we found a higher Delta-specific antibody response at the start of quarantine period, which correlated with higher Delta pseudovirus neutralizing capacity. Our findings indicate that a higher basal variant-specific antibody response in the mRNA-vaccinated individuals contributes to better protection against infections by the new emerging SARS-CoV-2 variants.

CD4+ and CD8+ T cells and antibodies are associated with protection against Delta vaccine breakthrough infection: a nested case-control study within the PITCH study

IMPORTANCE

Defining correlates of protection against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccine breakthrough infection informs vaccine policy for booster doses and future vaccine designs. Existing studies demonstrate humoral correlates of protection, but the role of T cells in protection is still unclear. In this study, we explore antibody and T cell immune responses associated with protection against Delta variant vaccine breakthrough infection in a well-characterized cohort of UK Healthcare Workers (HCWs). We demonstrate evidence to support a role for CD4+ and CD8+ T cells as well as antibodies against Delta vaccine breakthrough infection. In addition, our results suggest a potential role for cross-reactive T cells in vaccine breakthrough.

Navigating the Post-COVID-19 Immunological Era: Understanding Long COVID-19 and Immune Response

The COVID-19 pandemic has affected the world unprecedentedly, with both positive and negative impacts. COVID-19 significantly impacted the immune system, and understanding the immunological consequences of COVID-19 is essential for developing effective treatment strategies. The purpose of this review is to comprehensively explore and provide insights into the immunological aspects of long COVID-19, a phenomenon where individuals continue to experience a range of symptoms and complications, even after the acute phase of COVID-19 infection has subsided. The immune system responds to the initial infection by producing various immune cells and molecules, including antibodies, T cells, and cytokines. However, in some patients, this immune response becomes dysregulated, leading to chronic inflammation and persistent symptoms. Long COVID-19 encompasses diverse persistent symptoms affecting multiple organ systems, including the respiratory, cardiovascular, neurological, and gastrointestinal systems. In the post-COVID-19 immunological era, long COVID-19 and its impact on immune response have become a significant concern. Post-COVID-19 immune pathology, including autoimmunity and immune-mediated disorders, has also been reported in some patients. This review provides an overview of the current understanding of long COVID-19, its relationship to immunological responses, and the impact of post-COVID-19 immune pathology on patient outcomes. Additionally, the review addresses the current and potential treatments for long COVID-19, including immunomodulatory therapies, rehabilitation programs, and mental health support, all of which aim to improve the quality of life for individuals with long COVID-19. Understanding the complex interplay between the immune system and long COVID-19 is crucial for developing targeted therapeutic strategies and providing optimal care in the post-COVID-19 era.

Immune response after two doses of the BNT162b2 COVID-19 vaccine and risk of SARS-CoV-2 breakthrough infection in Tyrol, Austria: an open-label, observational phase 4 trial

BACKGROUND

Correlates of protection could help to assess the extent to which a person is protected from SARS-CoV-2 infection after vaccination (so-called breakthrough infection). We aimed to clarify associations of antibody and T-cell responses after vaccination against COVID-19 with risk of a SARS-CoV-2 breakthrough infection and whether measurement of these responses enhances risk prediction.

METHODS

We did an open-label, phase 4 trial in two community centres in the Schwaz district of the Federal State of Tyrol, Austria, before the emergence of the omicron (B.1.1.529) variant of SARS-CoV-2. We included individuals (aged ≥16 years) a mean of 35 days (range 27-43) after they had received a second dose of the BNT162b2 (Pfizer-BioNTech) COVID-19 vaccine. We quantified associations between immunological parameters and breakthrough infection and assessed whether information on these parameters improves risk discrimination. The study is registered with the European Union Drug Regulating Authorities Clinical Trials Database, 2021-002030-16.

FINDINGS

2760 individuals (1682 [60·9%] female, 1078 [39·1%] male, mean age 47·4 years [SD 14·5]) were enrolled into this study between May 15 and May 21, 2021, 712 (25·8%) of whom had a previous SARS-CoV-2 infection. Over a median follow-up of 5·9 months, 68 (2·5%) participants had a breakthrough infection. In models adjusted for age, sex, and previous infection, hazard ratios for breakthrough infection for having twice the immunological parameter level at baseline were 0·72 (95% CI 0·60-0·86) for anti-spike IgG, 0·80 (0·70-0·92) for neutralising antibodies in a surrogate virus neutralisation assay, 0·84 (0·58-1·21) for T-cell response after stimulation with a CD4 peptide pool, and 0·77 (0·54-1·08) for T-cell response after stimulation with a combined CD4 and CD8 peptide pool. For neutralising antibodies measured in a nested case-control sample using a pseudotyped virus neutralisation assay, the corresponding odds ratio was 0·78 (0·62-1·00). Among participants with previous infection, the corresponding hazard ratio was 0·73 (0·61-0·88) for anti-nucleocapsid Ig. Addition of anti-spike IgG information to a model containing information on age and sex improved the C-index by 0·085 (0·027-0·143).

INTERPRETATION

In contrast to T-cell response, higher levels of binding and neutralising antibodies were associated with a reduced risk of breakthrough SARS-CoV-2 infection. The assessment of anti-spike IgG enhances the prediction of incident breakthrough SARS-CoV-2 infection and could therefore be a suitable correlate of protection in practice. Our phase 4 trial measured both humoral and cellular immunity and had a 6-month follow-up period; however, the longer-term protection against emerging variants of SARS-CoV-2 remains unclear.

FUNDING

None.

The role of immune activation and antigen persistence in acute and long COVID

In late 2019, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) triggered the global coronavirus disease 2019 (COVID-19) pandemic. Although most infections cause a self-limited syndrome comparable to other upper respiratory viral pathogens, a portion of individuals develop severe illness leading to substantial morbidity and mortality. Furthermore, an estimated 10%-20% of SARS-CoV-2 infections are followed by post-acute sequelae of COVID-19 (PASC), or long COVID. Long COVID is associated with a wide variety of clinical manifestations including cardiopulmonary complications, persistent fatigue, and neurocognitive dysfunction. Severe acute COVID-19 is associated with hyperactivation and increased inflammation, which may be an underlying cause of long COVID in a subset of individuals. However, the immunologic mechanisms driving long COVID development are still under investigation. Early in the pandemic, our group and others observed immune dysregulation persisted into convalescence after acute COVID-19. We subsequently observed persistent immune dysregulation in a cohort of individuals experiencing long COVID. We demonstrated increased SARS-CoV-2-specific CD4+ and CD8+ T-cell responses and antibody affinity in patients experiencing long COVID symptoms. These data suggest a portion of long COVID symptoms may be due to chronic immune activation and the presence of persistent SARS-CoV-2 antigen. This review summarizes the COVID-19 literature to date detailing acute COVID-19 and convalescence and how these observations relate to the development of long COVID. In addition, we discuss recent findings in support of persistent antigen and the evidence that this phenomenon contributes to local and systemic inflammation and the heterogeneous nature of clinical manifestations seen in long COVID.

Breakthrough infections due to SARS-CoV-2 Delta variant: relation to humoral and cellular vaccine responses

Introduction

COVID-19 vaccines are expected to provide effective protection. However, emerging strains can cause breakthrough infection in vaccinated individuals. The immune response of vaccinated individuals who have experienced breakthrough infection is still poorly understood.

Methods

Here, we studied the humoral and cellular immune responses of fully vaccinated individuals who subsequently experienced breakthrough infection due to the Delta variant of SARS-CoV-2 and correlated them with the severity of the disease.

Results

In this study, an effective humoral response alone was not sufficient to induce effective immune protection against severe breakthrough infection, which also required effective cell-mediated immunity to SARS-CoV-2. Patients who did not require oxygen had significantly higher specific (p=0.021) and nonspecific (p=0.004) cellular responses to SARS-CoV-2 at the onset of infection than those who progressed to a severe form.

Discussion

Knowing both humoral and cellular immune response could allow to adapt preventive strategy, by better selecting patients who would benefit from additional vaccine boosters.

Trial registration numbers

https://clinicaltrials.gov, identifier NCT04355351; https://clinicaltrials.gov, identifier NCT04429594.

Tracking B Cell Memory to SARS-CoV-2 Using Rare Cell Analysis System

Rapid mutations within SARS-CoV-2 are driving immune escape, highlighting the need for in-depth and routine analysis of memory B cells (MBCs) to complement the important but limited information from neutralizing antibody (nAb) studies. In this study, we collected plasma samples and peripheral blood mononuclear cells (PBMCs) from 35 subjects and studied the nAb titers and the number of antigen-specific memory B cells at designated time points before and after vaccination. We developed an assay to use the MiSelect R II System with a single-use microfluidic chip to directly detect the number of spike-receptor-binding domain (RBD)-specific MBCs in PBMCs. Our results show that the number of spike-RBD-specific MBCs detected by the MiSelect R II System is highly correlated with the level of nAbs secreted by stimulated PBMCs, even 6 months after vaccination when nAbs were generally not present in plasma. We also found antigen-specific cells recognizing Omicron spike-RBD were present in PBMCs from booster vaccination of subjects, but with a high variability in the number of B cells. The MiSelect R II System provided a direct, automated, and quantitative method to isolate and analyze subsets of rare cells for tracking cellular immunity in the context of a rapidly mutating virus.

B-cell ELISpot assay to analyze human memory B cell and plasmablast responses specific to SARS-CoV-2 receptor-binding domain

B-cell ELISpot is an extremely sensitive assay based on the secretion of antibodies by B cells that requires the differentiation of B cells into antibody-secreting cells. Here, we describe the procedure to analyze both plasmablast (PB) and memory B cell (MBC) responses specific to SARS-CoV-2 receptor-binding domain (RBD) in the context of acute SARS-CoV-2 infection and vaccination. We detail steps for MBC stimulation, MBC and PB plating, detection, and counting of total IgG and RBD-specific spots. For complete details on the use and execution of this protocol, please refer to Tay et al. (2022).1.

Low humoral and cellular immune responses early after breakthrough infection may contribute to severe COVID-19

Background

Little is known about the immune determinants for severe coronavirus disease 2019 (COVID-19) in individuals vaccinated against severe acute respiratory syndrome coronavirus 2. We therefore attempted to identify differences in humoral and cellular immune responses between patients with non-severe and severe breakthrough COVID-19.

Methods

We prospectively enrolled hospitalized patients with breakthrough COVID-19 (severe and non-severe groups) and uninfected individuals who were vaccinated at a similar time (control group). Severe cases were defined as those who required oxygen therapy while hospitalized. Enzyme-linked immunosorbent assays and flow cytometry were used to evaluate humoral and cellular immune responses, respectively.

Results

Anti-S1 IgG titers were significantly lower in the severe group than in the non-severe group within 1 week of symptom onset and higher in the non-severe group than in the control group. Compared with the control group, the cellular immune response tended to be diminished in breakthrough cases, particularly in the severe group. In multivariate analysis, advanced age and low anti-S1 IgG titer were associated with severe breakthrough COVID-19.

Conclusions

Severe breakthrough COVID-19 might be attributed by low humoral and cellular immune responses early after infection. In the vaccinated population, delayed humoral and cellular immune responses may contribute to severe breakthrough COVID-19.

Efficient recall of SARS-CoV-2 variant-reactive B cells and T responses in the elderly upon heterologous mRNA vaccines as boosters

Waning antibody levels against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and the emergence of variants of concern highlight the need for booster vaccinations. This is particularly important for the elderly population, who are at a higher risk of developing severe coronavirus disease 2019 (COVID-19) disease. While studies have shown increased antibody responses following booster vaccination, understanding the changes in T and B cell compartments induced by a third vaccine dose remains limited. We analyzed the humoral and cellular responses in subjects who received either a homologous messenger RNA(mRNA) booster vaccine (BNT162b2 + BNT162b2 + BNT162b2; ''BBB") or a heterologous mRNA booster vaccine (BNT162b2 + BNT162b2 + mRNA-1273; ''BBM") at Day 0 (prebooster), Day 7, and Day 28 (postbooster). Compared with BBB, elderly individuals (≥60 years old) who received the BBM vaccination regimen display higher levels of neutralizing antibodies against the Wuhan and Delta strains along with a higher boost in immunoglobulin G memory B cells, particularly against the Omicron variant. Circulating T helper type 1(Th1), Th2, Th17, and T follicular helper responses were also increased in elderly individuals given the BBM regimen. While mRNA vaccines increase antibody, T cell, and B cell responses against SARS-CoV-2 1 month after receiving the third dose booster, the efficacy of the booster vaccine strategies may vary depending on age group and regimen combination.

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.

COVID-19 in patients with B cell immune deficiency

This article aims to describe the clinical manifestations and management of COVID-19 in patients with primary and secondary B cell deficient states. We describe the epidemiologic and clinical features as well as unique management paradigm including isolation precautions with COVID-19. We then focus upon primary and secondary preventive approaches including vaccination and pre- as well as post-exposure prophylaxis. Further, we elaborate upon the important disease specific risk factors in these patients and the need to conduct prospective clinical trials to develop individualized management strategies in this population.

Magnitude of venous or capillary blood-derived SARS-CoV-2-specific T cell response determines COVID-19 immunity

T cells specific for SARS-CoV-2 are thought to protect against infection and development of COVID-19, but direct evidence for this is lacking. Here, we associated whole-blood-based measurement of SARS-CoV-2-specific interferon-γ-positive T cell responses with positive COVID-19 diagnostic (PCR and/or lateral flow) test results up to 6 months post-blood sampling. Amongst 148 participants donating venous blood samples, SARS-CoV-2-specific T cell response magnitude is significantly greater in those who remain protected versus those who become infected (P < 0.0001); relatively low magnitude T cell response results in a 43.2% risk of infection, whereas high magnitude reduces this risk to 5.4%. These findings are recapitulated in a further 299 participants testing a scalable capillary blood-based assay that could facilitate the acquisition of population-scale T cell immunity data (14.9% and 4.4%, respectively). Hence, measurement of SARS-CoV-2-specific T cells can prognosticate infection risk and should be assessed when monitoring individual and population immunity status.

The role of B cells in COVID-19 infection and vaccination

B cells secrete antibodies and mediate the humoral immune response, making them extremely important in protective immunity against SARS-CoV-2, which caused the coronavirus disease 2019 (COVID-19) pandemic. In this review, we summarize the positive function and pathological response of B cells in SARS-CoV-2 infection and re-infection. Then, we structure the immunity responses that B cells mediated in peripheral tissues. Furthermore, we discuss the role of B cells during vaccination including the effectiveness of antibodies and memory B cells, viral evolution mechanisms, and future vaccine development. This review might help medical workers and researchers to have a better understanding of the interaction between B cells and SARS-CoV-2 and broaden their vision for future investigations.

Heterologous booster vaccination with CoronaVac following prime vaccination with mRNA vaccine

Objective

Despite the high vaccine efficacy of mRNA COVID‐19 vaccines, there are individuals who developed excessive reactogenic and/or allergic responses after the first mRNA dose and were considered ineligible for further mRNA doses. CoronaVac, an inactivated SARS‐CoV‐2 vaccine, is recommended in Singapore as an alternative.

Methods

Individuals, ineligible for further mRNA vaccines (BNT162b2 or mRNA‐1273) because of excessive reactive responses to prime mRNA vaccination, were recruited and offered two doses of CoronaVac as booster vaccination 38–224 days post their mRNA vaccine dose. Individuals who did not develop any excessive reactive responses after the prime mRNA vaccination were also recruited and given another mRNA vaccine as booster vaccination. Blood samples were collected at days 0, 21 and 90 post first CoronaVac dose and mRNA dose, respectively, for analysis.

Results

We showed that two CoronaVac booster doses induced specific immunity in these mRNA vaccine‐primed individuals. Although the spike‐specific antibody response was lower, their memory B cell response against the receptor‐binding domain (RBD) of the spike protein was similar, compared with individuals who received two BNT162b2 injections. The spike‐specific memory T cell response also increased following CoronaVac booster doses. However, specific immunity against the Omicron variant was low, similar to individuals with two BNT162b2 doses.

Conclusion

Our findings showed that while mRNA vaccine‐primed individuals can opt for two subsequent doses of CoronaVac, an additional dose may be necessary to achieve protection, especially against newly emerging immune escape variants such as Omicron.

Lower vaccine-acquired immunity in the elderly population following two-dose BNT162b2 vaccination is alleviated by a third vaccine dose

Understanding the impact of age on vaccinations is essential for the design and delivery of vaccines against SARS-CoV-2. Here, we present findings from a comprehensive analysis of multiple compartments of the memory immune response in 312 individuals vaccinated with the BNT162b2 SARS-CoV-2 mRNA vaccine. Two vaccine doses induce high antibody and T cell responses in most individuals. However, antibody recognition of the Spike protein of the Delta and Omicron variants is less efficient than that of the ancestral Wuhan strain. Age-stratified analyses identify a group of low antibody responders where individuals ≥60 years are overrepresented. Waning of the antibody and cellular responses is observed in 30% of the vaccinees after 6 months. However, age does not influence the waning of these responses. Taken together, while individuals ≥60 years old take longer to acquire vaccine-induced immunity, they develop more sustained acquired immunity at 6 months post-vaccination. A third dose strongly boosts the low antibody responses in the older individuals against the ancestral Wuhan strain, Delta and Omicron variants.

Persistence of MERS-CoV-spike-specific B cells and antibodies after late third immunization with the MVA-MERS-S vaccine

The Middle East respiratory syndrome (MERS) is a respiratory disease caused by MERS coronavirus (MERS-CoV). In follow up to a phase 1 trial, we perform a longitudinal analysis of immune responses following immunization with the modified vaccinia virus Ankara (MVA)-based vaccine MVA-MERS-S encoding the MERS-CoV-spike protein. Three homologous immunizations were administered on days 0 and 28 with a late booster vaccination at 12 ± 4 months. Antibody isotypes, subclasses, and neutralization capacity as well as T and B cell responses were monitored over a period of 3 years using standard and bead-based enzyme-linked immunosorbent assay (ELISA), 50% plaque-reduction neutralization test (PRNT50), enzyme-linked immunospot (ELISpot), and flow cytometry. The late booster immunization significantly increases the frequency and persistence of spike-specific B cells, binding immunoglobulin G1 (IgG1) and neutralizing antibodies but not T cell responses. Our data highlight the potential of a late boost to enhance long-term antibody and B cell immunity against MERS-CoV. Our findings on the MVA-MERS-S vaccine may be of relevance for coronavirus 2019 (COVID-19) vaccination strategies.

Characteristics of COVID-19 Breakthrough Infections among Vaccinated Individuals and Associated Risk Factors: A Systematic Review

We sought to assess breakthrough SARS-CoV-2 infections in vaccinated individuals by variant distribution and to identify the common risk associations. The PubMed, Web of Science, ProQuest, and Embase databases were searched from 2019 to 30 January 2022. The outcome of interest was breakthrough infections (BTIs) in individuals who had completed a primary COVID-19 vaccination series. Thirty-three papers were included in the review. BTIs were more common among variants of concern (VOC) of which Delta accounted for the largest number of BTIs (96%), followed by Alpha (0.94%). In addition, 90% of patients with BTIs recovered, 11.6% were hospitalized with mechanical ventilation, and 0.6% resulted in mortality. BTIs were more common in healthcare workers (HCWs) and immunodeficient individuals with a small percentage found in fully vaccinated healthy individuals. VOC mutations were the primary cause of BTIs. Continued mitigation approaches (e.g., wearing masks and social distancing) are warranted even in fully vaccinated individuals to prevent transmission. Further studies utilizing genomic surveillance and heterologous vaccine regimens to boost the immune response are needed to better understand and control BTIs.

Distinct Homologous and Variant-Specific Memory B-Cell and Antibody Response Over Time after SARS-CoV-2 mRNA Vaccination

The durability of protective humoral immunity after SARS-CoV-2 vaccination and infection is largely dependent on the generation and persistence of antigen-specific isotype-switched memory B cells (MBCs) and long-lived plasma cells that reside in the bone marrow and secrete high-affinity neutralizing antibodies. The reactivity of vaccine-induced MBCs to emerging clinically significant SARS-CoV-2 variants of concern (VoCs) is largely unknown. In a longitudinal cohort study (up to 6 months following COVID-19 mRNA vaccination) we measured MBCs in concert with other functional antibody measures. We found statistically significant differences between the frequencies of MBCs responding to homologous and VoC receptor-binding domain/RBDs (Beta, Gamma, and Delta) after vaccination that persisted over time. In concert with a waning antibody response, the reduced MBC response to VoCs could translate to a weaker subsequent recall immune response and increased susceptibility to the emerging SARS-CoV-2 variant strains after vaccination.