High Titers of Low Affinity Antibodies in COVID-19 Patients Are Associated With Disease Severity

SARS-CoV-2 humoral immune responses in convalescent individuals over 12 months reveal severity-dependent antibody dynamics

BACKGROUND

Defining the kinetics of SARS-CoV-2 antibody responses is critical for informing the management of reinfections, vaccinations, and therapeutics of Coronavirus disease 2019 (COVID-19).

METHODS

Using four antibody assays, we evaluated antibody titers against SARS-CoV-2 nucleocapsid (N), spike (S), and receptor binding domain (RBD) in 98 convalescent participants with varying COVID-19 disease severities (asymptomatic, mild, moderate or severe) at 1, 3, 6, and 12-months post-SARS-CoV-2-positive PCR and in 17 non-vaccinated, non-infected controls.

RESULTS

Increasing acute COVID-19 disease severity correlates with higher anti-N and anti-RBD titers throughout 12 months post-infection. Anti-N and anti-RBD titers decline over time in all participants, except for increased anti-RBD titers post-vaccination, with hospitalized participants exhibiting faster decay rates. Less than 50% of participants retain anti-N titers above controls at 12 months, with non-hospitalized participants falling below controls sooner. Nearly all participants maintain anti-RBD titers above controls for 12 months, suggesting long-term protection against severe reinfections. Nonetheless, by 6 months, few participants retain >50% of their initial 1-month anti-N or anti-RBD titers. Notably, vaccine-induced anti-RBD titers are higher in non-hospitalized participants. Lastly, early convalescent titers correlate with age but not with Post-Acute Sequelae of SARS-CoV-2 infection (PASC) status or steroid use.

CONCLUSION

Hospitalized participants initially develop higher anti-SARS-CoV-2 antibody titers that decline faster relative to non-hospitalized participants. While anti-N titers fall below control levels in some participants, anti-RBD titers remain above controls over 12 months, demonstrating long-lived antibody responses known to protect against severe disease. These findings advance our understanding of COVID-19 antibody dynamics.

Comprehensive analysis of human coronavirus antibody responses in ICU and non-ICU COVID-19 patients reveals IgG3 against SARS-CoV-2 spike protein as a key biomarker of disease severity

Introduction. Pre-existing immunity to human coronaviruses (HCoVs) may shape the immune response in COVID-19 patients. Increasing evidence suggests that immune cross-reactivity between SARS-CoV-2 and other coronaviruses may determine clinical prognosis.Hypothesis. SARS-CoV-2 disease severity is influenced by pre-existing immunity to HCoVs, with distinct antibody profiles and cross-reactivity patterns.Aim. To investigate the antibody response of ICU and non-ICU SARS-CoV-2 patients against different HCoV proteins and assess the potential impact of pre-existing immunity on SARS-CoV-2 disease outcomes.Methodology. This study used a comprehensive HCoVs antigen bead array to measure antibody response to pathogenic Middle East respiratory syndrome coronavirus (MERS-CoV), SARS-CoV, SARS-CoV-2 and the four seasonal HCoVs in 70 ICU and 63 non-ICU COVID-19 patients.Results. Our analysis demonstrates an overall higher antibody response in ICU than in non-ICU COVID-19 patients. Interestingly, the anti-S1 IgG and IgA were significantly higher among ICU than in non-ICU patients. Similarly, the anti-S1 IgG against NL63 showed a lower response among ICU compared to non-ICU. Cross-reactivity was evident between SARS-CoV-2 and SARS-CoV antibodies but not with MERS-CoV and seasonal HCoVs. The subclass analysis of antibodies recognizing SARS-CoV-2 revealed that anti-S1 IgG1, IgG3, IgA1 and IgA2 were significantly higher in ICU compared to non-ICU. The predominant IgA subtype among SARS-CoV-2 patients was IgA1. We applied machine learning algorithms to subclass serological responses to build classifiers that could distinguish between ICU patients and patients with milder COVID-19. Out of 90 variables used in two different types of models, the variable of highest influence in determining the ICU status was IgG3 against SARS-CoV-2 S, and the top 8 variables of influence included the presence of IgG3 against S-trimer as well as IgA against SARS-CoV-2 S.Conclusion. Understanding the complexities of humoral immunity in various patients is critical for early medical intervention, disease management, selective vaccination and passive immunotherapy.

SARS-CoV-2 S1 protein induces IgG-mediated platelet activation and is prevented by 1.8-cineole

COVID-19 patients face an increased risk of thromboembolic complications, yet the exact pathophysiological role of platelets in the disease remains unclear. Considering the multifaceted nature of COVID-19 symptoms, including platelet hyperactivation and inflammation, the development of compounds that simultaneously target both represents a promising therapeutic strategy. The monoterpene 1.8-cineole (CNL-1976) is known for its anti-inflammatory and anti-aggregatory effects. Thus, understanding the mechanism behind platelet hyperactivation and the effect of 1.8-cineole during COVID-19 is crucial when aiming for a reduction of disease severity. In this study, we investigated the mechanism of platelet activation triggered by the SARS-CoV-2 S1 spike protein (S1). Utilizing S1-coupled beads, we discovered that platelet activation and aggregation were dependent on plasma components, particularly S1-specific IgG antibodies. The formation of immune complexes through IgG binding to S1 facilitated the crosslinking of the platelet expressed FcγRIIa receptor, initiating platelet activation and aggregation, as well as formation of platelet-leukocyte aggregates (PLAs). Importantly, treatment with 1.8-cineole significantly inhibited S1-bead-induced platelet activity and PLA formation. These findings strongly suggest that antibody-mediated platelet activation via FcγRIIa directly contributes to the well-recognized prothrombotic environment during COVID-19. Moreover, our data indicate that 1.8-cineole can serve as a potential therapeutic compound, alleviating platelet-driven thromboinflammatory complications associated with COVID-19 and post-acute sequelae of SARS-CoV-2 (PASC).

Antibody Avidity Maturation Following Booster Vaccination with an Intranasal Adenovirus Salnavac Vaccine

BACKGROUND

The COVID-19 pandemic has led to the rapid development of new vaccines and methods of testing vaccine-induced immunity. Despite the extensive research that has been conducted on the level of specific antibodies, less attention has been paid to studying the avidity of these antibodies. The avidity of serum antibodies is associated with a vaccine showing high effectiveness and reflects the process of affinity maturation. In the context of vaccines against SARS-CoV-2, only a limited number of studies have investigated the avidity of antibodies, often solely focusing on the wild-type virus following vaccination. This study provides new insights into the avidity of serum antibodies following adenovirus-based boosters. We focused on the effects of an intranasal Salnavac booster, which is compared, using a single analytical platform, to an intramuscular Sputnik V.

METHODS

The avidity of RBD-specific IgGs and IgAs was investigated through ELISA using urea and biolayer interferometry.

RESULTS

The results demonstrated the similar avidities of serum antibodies, which were induced by both vaccines for six months post-booster. However, an increase in antibody avidity was observed for the wild-type and Delta variants, but not for the BA.4/5 variant.

CONCLUSIONS

Collectively, our data provide the insights into antibody avidity maturation after the adenovirus-based vaccines against SARS-CoV-2.

Control of complement-induced inflammatory responses to SARS-CoV-2 infection by anti-SARS-CoV-2 antibodies

Dysregulated immune responses contribute to the excessive and uncontrolled inflammation observed in severe COVID-19. However, how immunity to SARS-CoV-2 is induced and regulated remains unclear. Here, we uncover the role of the complement system in the induction of innate and adaptive immunity to SARS-CoV-2. Complement rapidly opsonizes SARS-CoV-2 particles via the lectin pathway. Complement-opsonized SARS-CoV-2 efficiently induces type-I interferon and pro-inflammatory cytokine responses via activation of dendritic cells, which are inhibited by antibodies against the complement receptors (CR) 3 and 4. Serum from COVID-19 patients, or monoclonal antibodies against SARS-CoV-2, attenuate innate and adaptive immunity induced by complement-opsonized SARS-CoV-2. Blocking of CD32, the FcγRII antibody receptor of dendritic cells, restores complement-induced immunity. These results suggest that opsonization of SARS-CoV-2 by complement is involved in the induction of innate and adaptive immunity to SARS-CoV-2 in the acute phase of infection. Subsequent antibody responses limit inflammation and restore immune homeostasis. These findings suggest that dysregulation of the complement system and FcγRII signaling may contribute to severe COVID-19.

Applications of SARS-CoV-2 serological testing: impact of test performance, sample matrices, and patient characteristics

Laboratory testing has been a key tool in managing the SARS-CoV-2 global pandemic. While rapid antigen and PCR testing has proven useful for diagnosing acute SARS-CoV-2 infections, additional testing methods are required to understand the long-term impact of SARS-CoV-2 infections on immune response. Serological testing, a well-documented laboratory practice, measures the presence of antibodies in a sample to uncover information about host immunity. Although proposed applications of serological testing for clinical use have previously been limited, current research into SARS-CoV-2 has shown growing utility for serological methods in these settings. To name a few, serological testing has been used to identify patients with past infections and long-term active disease and to monitor vaccine efficacy. Test utility and result interpretation, however, are often complicated by factors that include poor test sensitivity early in infection, lack of immune response in some individuals, overlying infection and vaccination responses, lack of standardization of antibody titers/levels between instruments, unknown titers that confer immune protection, and large between-individual biological variation following infection or vaccination. Thus, the three major components of this review will examine (1) factors that affect serological test utility: test performance, testing matrices, seroprevalence concerns and viral variants, (2) patient factors that affect serological response: timing of sampling, age, sex, body mass index, immunosuppression and vaccination, and (3) informative applications of serological testing: identifying past infection, immune surveillance to guide health practices, and examination of protective immunity. SARS-CoV-2 serological testing should be beneficial for clinical care if it is implemented appropriately. However, as with other laboratory developed tests, use of SARS-CoV-2 serology as a testing modality warrants careful consideration of testing limitations and evaluation of its clinical utility.

Hematological, inflammatory, and novel biomarkers assessment as an eminent strategy for clinical management of COVID-19

BACKGROUND

Different biomarkers have been suggested as novel biomarkers of coronavirus disease 2019 (COVID-19) theragnosis. With the aim of having a better clinical management of COVID-19, we decided to determine the relationship between hematological, inflammatory, and novel biomarkers with severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) immunoglobulin (Ig)M and IgG antibodies.

METHODS

Blood samples from 127 confirmed COVID-19 patients aged 11-84 years old were collected and tested for SARS-CoV-2 IgM and IgG antibodies alongside with hematological, inflammatory, and novel biomarkers. The Spearman correlation test was utilized to analyze the correlation between these biomarkers with SARS-CoV-2 IgM and IgG antibodies.

RESULTS

The SARS-CoV-2 IgM antibody significantly correlated with erythrocyte sedimentation rate (ESR) (r = 0.329, p = 0.000), C-reactive protein (CRP) (r = 0.459, p = 0.000), interleukin (IL)-6 (r = 0.345, p = 0.000), IL-8 (r = 0.263, p = 0.003), neutrophil to lymphocyte ratio (NLR) (r = 0.182, p = 0.040), derived NLR (dNLR) (r = 0.197, p = 0.026), neutrophil to monocyte ratio (NMR) (r = 0.184, p = 0.038), and CRP to lymphocyte ratio (CLR) (r = 0.495, p = 0.000). Also, we find significant correlation between SARS-CoV-2 IgG antibody with hemoglobin (Hb) (r = -0.257, p = 0.004), hematocrit (Hct) (r = -0.227, p = 0.010), mean corpuscular Hb concentration (MCHC) (r = -0.212, p = 0.017), lymphocyte count (r = -0.211, p = 0.017), platelet count (r = 0.179, p = 0.044), ESR (r = 0.461, p = 0.000), CRP (r = 0.344, p = 0.000), IL-6 (r = 0.178, p = 0.046), IL-8 (r = 0.237, p = 0.007), platelet to lymphocyte ratio (PLR) (r = 0.295, p = 0.001), and CLR (r = 0.376, p = 0.000).

CONCLUSION

Hematological biomarkers (Hb, Hct, MCHC, lymphocyte count, and platelet count), inflammatory biomarkers (ESR, CRP, IL-6, and IL-8), and novel biomarkers (dNLR, NLR, NMR, PLR, and CLR) are valuable indicators for clinical management of COVID-19.

Longitudinal Analysis of Antibody Response Following SARS-CoV-2 Infection Depending on Disease Severity: A Prospective Cohort Study

OBJECTIVE

Severe coronavirus disease 19 (COVID-19) is characterized by a dysregulated inflammatory response, with humoral immunity playing a central role in the disease course. The objective of this study was to assess the immune response and the effects of vaccination in recovered individuals with variable disease severity up to one year following natural infection.

METHODS

A prospective cohort study was conducted including patients with laboratory-confirmed COVID-19. Disease severity was classified as mild, moderate, and severe based on clinical presentation and outcomes. Anti-RBD (receptor binding domain) and neutralizing antibodies were evaluated at multiple timepoints during the first year after COVID-19 diagnosis.

RESULTS

A total of 106 patients were included; of them, 28 were diagnosed with mild, 38 with moderate, and 40 with severe disease. At least one vaccine dose was administered in 58 individuals during the follow-up. Participants with mild disease presented significantly lower anti-RBD and neutralizing antibodies compared to those with moderate and severe disease up to the 3rd and 6th months after the infection, respectively. After adjusting for covariates, in the third month, severe COVID-19 was associated with significantly higher anti-RBD (β: 563.09; 95% confidence intervals (CI): 257.02 to 869.17) and neutralizing (β: 21.47; 95% CI: 12.04 to 30.90) antibodies. Among vaccinated individuals, at the 12th month, a history of moderate disease was associated with significantly higher anti-RBD levels (β: 5615.19; 95% CI: 657.92 to 10,572.46).

CONCLUSIONS

Severe COVID-19 is associated with higher anti-RBD and neutralizing antibodies up to 6 months after the infection. Vaccination of recovered patients is associated with a remarkable augmentation of antibody titers up to one year after COVID-19 diagnosis, regardless of disease severity.

Comprehensive antibody and cytokine profiling in hospitalized COVID-19 patients in relation to clinical outcomes in a large Belgian cohort

The immune response in patients with Coronavirus Disease 2019 (COVID-19) is highly variable and is linked to disease severity and mortality. However, antibody and cytokine responses in the early disease stage and their association with disease course and outcome are still not completely understood. In this large, multi-centre cohort study, blood samples of 434 Belgian COVID-19 hospitalized patients with different disease severities (ranging from asymptomatic/mild to critically ill) from the first wave of the COVID-19 pandemic were obtained. Baseline antibody and cytokine responses were characterized and associations with several clinical outcome parameters were determined. Anti-spike immunoglobulin (Ig)G and IgM levels were elevated in patients with a more severe disease course. This increased baseline antibody response however was associated with decreased odds for hospital mortality. Levels of the pro-inflammatory cytokines IL-6, IP-10 and IL-8, the anti-inflammatory cytokine IL-10 and the antiviral cytokines IFN-α, IFN-β and IFN-λ1 were increased with disease severity. Remarkably, we found significantly lower levels of IFN-λ2,3 in critically ill patients compared to patients of the moderate and severe disease category. Finally, levels of IL-8, IL-6, IP-10, IL-10, IFN-α, IFN-β, IFN-γ and IFN-λ1 at baseline were positively associated with mortality, whereas higher IFN-λ2,3 levels were negatively associated with mortality.

Impaired immune response against SARS-CoV-2 infection is the major factor indirectly altering reproductive function in COVID-19 patients: a narrative review

Coronavirus disease 2019 (COVID-19) is an infectious disease affecting multiple systems and organs, including the reproductive system. SARS-CoV-2, the virus that causes COVID-19, can damage reproductive organs through direct (angiotensin converting enzyme-2, ACE-2) and indirect mechanisms. The immune system plays an essential role in the homeostasis and function of the male and female reproductive systems. Therefore, an altered immune response related to infectious and inflammatory diseases can affect reproductive function and fertility in both males and females. This narrative review discussed the dysregulation of innate and adaptive systems induced by SARS-CoV-2 infection. We reviewed the evidence showing that this altered immune response in COVID-19 patients is the major indirect mechanism leading to adverse reproduction outcomes in these patients. We summarized studies reporting the long-term effect of SARS-CoV-2 infection on women's reproductive function and proposed the chronic inflammation and chronic autoimmunity characterizing long COVID as potential underlying mechanisms. Further studies are needed to clarify the role of autoimmunity and chronic inflammation (long COVID) in altered female reproduction function in COVID-19.

Cross-reactive humoral and CD4+ T cell responses to Mu and Gamma SARS-CoV-2 variants in a Colombian population

The SARS CoV-2 antibody and CD4+ T cell responses induced by natural infection and/or vaccination decline over time and cross-recognize other viral variants at different levels. However, there are few studies evaluating the levels and durability of the SARS CoV-2-specific antibody and CD4+ T cell response against the Mu, Gamma, and Delta variants. Here, we examined, in two ambispective cohorts of naturally-infected and/or vaccinated individuals, the titers of anti-RBD antibodies and the frequency of SARS-CoV-2-specific CD4+ T cells up to 6 months after the last antigen exposure. In naturally-infected individuals, the SARS-CoV-2 antibody response declined 6 months post-symptoms onset. However, the kinetic observed depended on the severity of the disease, since individuals who developed severe COVID-19 maintained the binding antibody titers. Also, there was detectable binding antibody cross-recognition for the Gamma, Mu, and Delta variants, but antibodies poorly neutralized Mu. COVID-19 vaccines induced an increase in antibody titers 15-30 days after receiving the second dose, but these levels decreased at 6 months. However, as expected, a third dose of the vaccine caused a rise in antibody titers. The dynamics of the antibody response upon vaccination depended on the previous SARS-CoV-2 exposure. Lower levels of vaccine-induced antibodies were associated with the development of breakthrough infections. Vaccination resulted in central memory spike-specific CD4+ T cell responses that cross-recognized peptides from the Gamma and Mu variants, and their duration also depended on previous SARS-CoV-2 exposure. In addition, we found cross-reactive CD4+ T cell responses in unexposed and unvaccinated individuals. These results have important implications for vaccine design for new SARS-CoV-2 variants of interest and concern.

Predictors of high SARS-CoV-2 immunoglobulin G titers in COVID-19 convalescent whole-blood donors: a cross-sectional study in China

Background

Demographic information has been shown to help predict high antibody titers of COVID-19 convalescent plasma (CCP) in CCP donors. However, there is no research on the Chinese population and little evidence on whole-blood donors. Therefore, we aimed to investigate these associations among Chinese blood donors after SARS-CoV-2 infection.

Methods

In this cross-sectional study, 5,064 qualified blood donors with confirmed or suspected SARS-CoV-2 infection completed a self-reported questionnaire and underwent tests of SARS-CoV-2 Immunoglobulin G (IgG) antibody and ABO blood type. Logistic regression models were used to calculate odds ratios (ORs) for high SARS-CoV-2 IgG titers according to each factor.

Results

Totally, 1,799 participants (with SARS-CoV-2 IgG titers≥1:160) had high-titer CCPs. Multivariable analysis showed that a 10-year increment in age and earlier donation were associated with higher odds of high-titer CCP, while medical personnel was associated with lower odds. The ORs (95% CIs) of high-titer CCP were 1.17 (1.10-1.23, p< 0.001) and 1.41 (1.25-1.58, p< 0.001) for each 10-year increment in age and earlier donation, respectively. The OR of high-titer CCP was 0.75 (0.60-0.95, p = 0.02) for medical personnel. Female early donors were associated with increased odds of high-titer CCP, but this association was insignificant for later donors. Donating after 8 weeks from the onset was associated with decreased odds of having high-titer CCP compared to donating within 8 weeks from the onset, and the HR was 0.38 (95% CI: 0.22-0.64, p <0.001). There was no significant association between ABO blood type or race and the odds of high-titer CCP.

Discussion

Older age, earlier donation, female early donors, and non-medical-related occupations are promising predictors of high-titer CCP in Chinese blood donors. Our findings highlight the importance of CCP screening at the early stage of the pandemic.

The quantity and quality of anti-SARS-CoV-2 antibodies show contrariwise association with COVID-19 severity: lessons learned from IgG avidity

Gaining more appreciation on the protective/damaging aspects of anti-SARS-CoV-2 immunity associated with disease severity is of great importance. This study aimed to evaluate the avidity of serum IgG antibodies against SARS-CoV-2 spike (S) and nucleocapsid (N) in hospitalized symptomatic COVID-19 patients and asymptomatic RT-PCR-confirmed SARS-CoV-2 carriers as well as to compare antibody avidities with respect to vaccination status, vaccination dose and reinfection status. Serum levels of anti-S and anti-N IgG were determined using specific ELISA kits. Antibody avidity was determined by urea dissociation assay and expressed as avidity index (AI) value. Despite higher IgG levels in the symptomatic group, AI values of both anti-S and anti-N IgG were significantly lower in this group compared to asymptomatic individuals. In both groups, anti-S AI values were elevated in one-dose and two-dose vaccinees versus unvaccinated subjects, although significant differences were only detected in the symptomatic group. However, anti-N avidity showed no significant difference between the vaccinated and unvaccinated subgroups. Almost all vaccinated patients of different subgroups (based on vaccine type) had higher anti-S IgG avidity, while the statistical significance was detected only between those receiving Sinopharm compared to the unvaccinated subgroup. Also, statistically significant differences in antibody AIs were only found between primarily infected individuals of the two groups. Our findings indicate a key role for anti-SARS-CoV-2 IgG avidity in protection from symptomatic COVID-19 and calls for the incorporation of antibody avidity measurement into the current diagnostic tests to predict effective immunity toward SARS-CoV-2 infection or even for prognostic purposes.

SARS-CoV-2 Spike and Nucleocapsid Antibody Response in Vaccinated Croatian Healthcare Workers and Infected Hospitalized Patients: A Single Center Cohort Study

Studies assessing the dynamics and duration of antibody responses following SARS-CoV-2 infection or vaccination are an invaluable tool for vaccination schedule planning, assessment of risk groups and management of pandemics. In this study, we developed and employed ELISA assays to analyze the humoral responses to Nucleocapsid and Spike proteins in vaccinated health-care workers (HCW) and critically ill COVID-19 patients. Sera of more than 1000 HCWs and critically ill patients from the Clinical Hospital Center Rijeka were tested across a one-year period, encompassing the spread of major SARS-CoV-2 variants of concern (VOCs). We observed 97% of seroconversion in HCW cohort as well as sustained anti-Spike antibody response in vaccinees for more than 6 months. In contrast, the infection-induced anti-Nucleocapsid response was waning significantly in a six-month period. Furthermore, a substantial decrease in vaccinees' anti-Spike antibodies binding to Spike protein of Omicron VOC was also observed. Critically ill COVID-19 patients had higher levels of anti-Spike and anti-Nucleocapsid antibodies compared to HCWs. No significant differences in anti-Spike and anti-Nucleocapsid antibody levels between the critically ill COVID-19 patients that were on non-invasive oxygen supplementation and those on invasive ventilation support were observed. However, stronger anti-Spike, but not anti-Nucleocapsid, antibody response correlated with a better disease outcome in the cohort of patients on invasive ventilation support. Altogether, our results contribute to the growing pool of data on humoral responses to SARS-CoV-2 infection and vaccination.

Evidence for deleterious effects of immunological history in SARS-CoV-2

A previous report demonstrated the strong association between the presence of antibodies binding to an epitope region from SARS-CoV-2 nucleocapsid, termed Ep9, and COVID-19 disease severity. Patients with anti-Ep9 antibodies (Abs) had hallmarks of antigenic interference (AIN), including early IgG upregulation and cytokine-associated injury. Thus, the immunological memory of a prior infection was hypothesized to drive formation of suboptimal anti-Ep9 Abs in severe COVID-19 infections. This study identifies a putative primary antigen capable of stimulating production of cross-reactive, anti-Ep9 Abs. Binding assays with patient blood samples directly show cross-reactivity between Abs binding to Ep9 and only one bioinformatics-derived, homologous putative antigen, a sequence derived from the neuraminidase protein of H3N2 influenza A virus. This cross-reactive binding is highly influenza strain specific and sensitive to even single amino acid changes in epitope sequence. The neuraminidase protein is not present in the influenza vaccine, and the anti-Ep9 Abs likely resulted from the widespread influenza infection in 2014. Therefore, AIN from a previous infection could underlie some cases of COVID-19 disease severity.

Antibody affinity and cross-variant neutralization of SARS-CoV-2 Omicron BA.1, BA.2 and BA.3 following third mRNA vaccination

There is limited knowledge on durability of neutralization capacity and antibody affinity maturation generated following two versus three doses of SARS-CoV-2 mRNA vaccines in naïve versus convalescent individuals (hybrid immunity) against the highly transmissible Omicron BA.1, BA.2 and BA.3 subvariants. Virus neutralization titers against the vaccine-homologous strain (WA1) and Omicron sublineages are measured in a pseudovirus neutralization assay (PsVNA). In addition, antibody binding and antibody affinity against spike proteins from WA1, BA.1, and BA.2 is determined using surface plasmon resonance (SPR). The convalescent individuals who after SARS-CoV-2 infection got vaccinated develop hybrid immunity that shows broader neutralization activity and cross-reactive antibody affinity maturation against the Omicron BA.1 and BA.2 after either second or third vaccination compared with naïve individuals. Neutralization activity correlates with antibody affinity against Omicron subvariants BA.1 and BA.2 spikes. Importantly, at four months post-third vaccination the neutralization activity and antibody affinity against the Omicron subvariants is maintained and trended higher for the individuals with hybrid immunity compared with naïve adults. These findings about hybrid immunity resulting in superior immune kinetics, breadth, and durable high affinity antibodies support the need for booster vaccinations to provide effective protection from emerging SARS-CoV-2 variants like the rapidly spreading Omicron subvariants.

Here the authors show that a third SARS-CoV-2 vaccination significantly boosts neutralizing antibodies against Omicron subvariants and that hybrid immunity (infection and vaccination) results in broader neutralization activity and cross-reactive antibody affinity maturation.