Comparison Of New and emerging SARS-CoV-2 variant Transmissibility through Active Contact Testing. A comparative cross-sectional household seroprevalence study.

Historically SARS-CoV-2 secondary attack rates (SAR) have been based on PCR positivity on screening symptomatic contacts, this misses transmission events and identifies only symptomatic contacts who are PCR positive at the time of sampling. We used serology to detect the relative transmissibility of Alpha Variant of Concern (VOC) to non-VOC SARS-CoV-2 to calculate household secondary attack rates. We identified index patients diagnosed with Alpha and non-VOC SARS-CoV-2 across two London Hospitals between November 2020 and January 2021 during a prolonged and well adhered national lockdown. We completed a household seroprevalence survey and found that 61.8% of non-VOC exposed household contacts were seropositive compared to 82.1% of Alpha exposed household contacts. The odds of infection doubled with exposure to an index diagnosed with Alpha. There was evidence of transmission events in almost all households. Our data strongly support that estimates of SAR should include serological data to improve accuracy and understanding. Key MessagesSecondary attack rates (SAR) in SARS-CoV-2 were previously calculated using PCR positive samples only, it is more accurate to use a household transmission model and screen contacts using serology, as done in this study. SAR should include serological data to improve accuracy and understanding. All households in this study had transmission events. SAR were 61.8% in non-VOC SARS-CoV-2 exposed household contacts compared to 82.1% in Alpha SARS-CoV-2 exposed household contacts.

Differential immune response induced by two immunization schedules with an inactivated SARS-CoV-2 vaccine in a randomized phase 3 clinical trial

BackgroundThe development of vaccines to control the COVID-19 pandemic progression is a worldwide priority. CoronaVac(R) is an inactivated SARS-CoV-2 vaccine approved for emergency use with robust efficacy and immunogenicity data reported in trials in China, Brazil, Indonesia, Turkey, and Chile. MethodsThis study is a randomized, multicenter, and controlled phase 3 trial in healthy Chilean adults aged [≥]18 years. Volunteers received two doses of CoronaVac(R) separated by two (0-14 schedule) or four weeks (0-28 schedule). 2,302 volunteers were enrolled, 440 were part of the immunogenicity arm, and blood samples were obtained at different times. Samples from a single center are reported. Humoral immune responses were evaluated by measuring the neutralizing capacities of circulating antibodies. Cellular immune responses were assessed by ELISPOT and flow cytometry. Correlation matrixes were performed to evaluate correlations in the data measured. ResultsBoth schedules exhibited robust neutralizing capacities with the response induced by the 0-28 schedule being better. No differences were found in the concentration of antibodies against the virus and different variants of concern between schedules. Stimulation of PBMCs with MPs induced the secretion of IFN-{gamma} and the expression of activation induced markers for both schedules. Correlation matrixes showed strong correlations between neutralizing antibodies and IFN-{gamma} secretion. ConclusionsImmunization with CoronaVac(R) in Chilean adults promotes robust cellular and humoral immune responses. The 0-28 schedule induced a stronger humoral immune response than the 0-14 schedule. FundingMinistry of Health, Government of Chile, Confederation of Production and Commerce & Millennium Institute on Immunology and Immunotherapy, Chile. Clinical trial numberNCT04651790. summaryTwo immunization schedules were evaluated for the inactivated SARS-CoV-2 vaccine, Coronavac(R), with two doses of the vaccine separated by two or four weeks. We compared humoral and cellular immune responses, showing they are mostly similar, with differences in neutralization capacities.

Hybrid immunity expands the functional humoral footprint of both mRNA and vector-based SARS-CoV-2 vaccines

The COVID-19 pandemic catalyzed a revolution in vaccine development, leading to the testing and approval of several global vaccine platforms that have shown tremendous promise in curbing the pandemic. Yet, despite these successes, waning immunity, and the emergence of variants of concern linked to rising breakthrough infections among vaccinees, have begun to highlight opportunities to improve vaccine platforms and deployment. Real-world vaccine efficacy has highlighted the reduced risk of breakthrough infection and disease among individuals infected and vaccinated, otherwise referred to as hybrid immunity. Hybrid immunity points to the potential for more vigorous or distinct immunity primed by the infection and may confer enhanced protection from COVID-19. Beyond augmented hybrid induced neutralizing antibody and T cell immune responses, here we sought to define whether hybrid immunity may shape the functional humoral immune response to SARS-CoV-2 following Pfizer/BNT162b2 and Moderna mRNA1273 mRNA-based, and ChadOx1/AZ1222 and Ad26.COV2.S vector-based SARS-CoV-2 vaccination. Each vaccine exhibited a unique functional humoral immune profile in the setting of naive or hybrid immunity. However, hybrid immunity showed a unique augmentation in S2-domain specific functional humoral immunity that was poorly induced in the setting of naive immune response. These data highlight the immunodominant effect of the S1-domain in the setting of natural immunity, which is highly variable during viral evolution, and the importance of natural infection in breaking this immunodominance in driving immunity to the S2 region of the SARS-CoV-2 S2 domain that is more conserved across variants of concern.

Natural and hybrid immunity following four COVID-19 waves in a South African cohort

BackgroundMore than half the global population has been exposed to SARS-CoV-2. Naturally induced immunity influences the outcome of subsequent exposure to variants and vaccine responses. We measured anti-spike IgG responses to explore the basis for this enhanced immunity. MethodsA prospective cohort study in a South African community through the ancestral/beta/delta/omicron SARS-CoV-2 waves. Health seeking behaviour/illness were recorded and post-wave serum samples probed for IgG to Spike (CoV2-S-IgG). To estimate protective CoV2-S-IgG threshold levels, logistic functions were fit to describe the correlation of CoV2-S-IgG measured before a wave and the probability for seroconversion/boosting thereafter for unvaccinated and vaccinated adults. FindingsDespite little disease, 176/339 (51{middle dot}9%) participants were seropositive following wave 1, rising to 74%, 89{middle dot}8% and 97{middle dot}3% after waves 2, 3 and 4 respectively. CoV2-S-IgG induced by natural exposure protected against subsequent SARS-CoV-2 infection with the greatest protection for beta and the least for omicron. Vaccination induced higher CoV2-S-IgG in seropositive compared to naive vaccinees. Amongst seropositive participants, proportions above the 50% protection against infection threshold were 69% (95% CrI: 62, 72) following 1 vaccine dose, 63% (95% CrI: 63, 75) following 2 doses and only 11% (95% CrI: 7, 14) in unvaccinated during the omicron wave. InterpretationNaturally induced CoV2-S-IgG do not achieve high enough levels to prevent omicron infection in most exposed individuals but are substantially boosted by vaccination leading to significant protection. A single vaccination in those with prior immunity is more immunogenic than 2 doses in a naive vaccinee and thus may provide adequate protection. FundingUK NIH GECO award (GEC111), Wellcome Trust Centre for Infectious Disease Research in Africa (CIDRI), Bill & Melinda Gates Foundation, USA (OPP1017641, OPP1017579) and NIH H3 Africa (U54HG009824, U01AI110466]. HZ is supported by the SA-MRC. MPN is supported by an Australian National Health and Medical Research Council Investigator Grant (APP1174455). BJQ is supported by a grant from the Bill and Melinda Gates Foundation (OPP1139859). Stefan Flasche is supported by a Sir Henry Dale Fellowship jointly funded by the Wellcome Trust and the Royal Society (Grant number 208812/Z/17/Z). Research in context Evidence before this studyNatural infection with ancestral SARS-CoV-2 virus provides partial protection against re-infection with the same and closely related SARS-CoV-2 variants, but higher rates of re-infection have been described with Omicron. In addition, vaccination against SARS-CoV2 provides relatively lower protection against symptomatic Omicron infection than for other variants. Hybrid immunity, a combination of immunity induced by natural infection and vaccination is of critical interest due to the high incidence of natural infection in many populations and increased availability of vaccination. Vaccination following infection may provide more robust immunity than either infection or vaccination alone, but there are limited data on the impact of hybrid immunity for protection against different variants or on the optimal vaccination strategy following natural infection. Added value of this studyWe leveraged a unique South African birth cohort in a poor peri-urban area, to longitudinally investigate infection, illness and serological responses to natural exposure to SARS-CoV-2 over 4 waves of the pandemic in healthy mothers. We also investigated the impact of prior natural exposure on BNT162b2 mRNA vaccine responses. We used this information to derive estimates of levels of spike-specific IgG associated with protection for subsequent infection following natural or hybrid immunity. Despite little disease, most participants were seropositive with rates rising from 52% to 74%, 90% and 97% after waves 1, 2, 3 and 4 respectively. Antibodies to spike protein induced by natural exposure protected against subsequent infection with the greatest protection for beta and the least for omicron. Antibody levels following vaccination were significantly higher in those who were seropositive prior to vaccine, compared to those seronegative. Amongst seropositive participants, proportions above the 50% protection against infection threshold were 69% following 1 vaccine dose, 63% following 2 doses and only 11% in unvaccinated during the omicron wave. In those seropositive prior to vaccination no significant increase in antibody levels occurred after the 2nd dose of vaccine, unlike the increase in seronegative participants. A single dose of vaccine in seropositive individuals induced higher antibody concentrations than two doses in seronegative recipients. Implications of all the available evidenceNaturally induced spike antibodies do not achieve high enough levels to prevent omicron infection in most exposed individuals but are substantially boosted by vaccination leading to significant protection. A single vaccination in those with prior natural immunity is more immunogenic than 2 doses in seronegative people and may provide adequate protection against omicron and other variants. Vaccination programs in populations with high seroprevalence using a single vaccination as a primary strategy should be considered.

High neutralizing antibody levels against SARS-CoV-2 Omicron after UB-612 booster vaccination

The highly transmissible Omicron variant has caused high rates of breakthrough infections among vaccinated and convalescent individuals. Here, we demonstrate that a booster dose of UB-612 vaccine candidate delivered 7-9 months after primary vaccination increases neutralizing antibody levels by 131-, 61- and 49-fold against ancestral SARS-CoV-2, Omicron BA.1 and BA.2 variants, respectively. Based on the RBD protein binding antibody responses, we estimated a [~]95% efficacy against symptomatic COVID-19 caused by the ancestral strain after a UB-612 booster. Our results support UB-612 vaccine as a potent booster against current and emerging SARS-CoV-2 variants.

Humoral and cellular responses to SARS-CoV-2 vaccination in patients with lymphoid malignancies

SARS-CoV-2 vaccination protects against COVID-19. Antibodies and antigen-specific T-cell responses against the spike domain can be used to measure vaccine immune response. Individuals with lymphoma have defects in humoral and cellular immunity that may compromise vaccine response. In this prospective observational study of 457 participants with lymphoma, 52% of participants vaccinated on treatment had undetectable anti-spike IgG antibodies compared to 9% who were not on treatment. Marked impairment was observed in those receiving anti- CD20 antibody within 12 months where 60% had undetectable antibodies compared to 11% on chemotherapy, which persisted despite three vaccine doses. Overall, 63% had positive T-cell responses irrespective of treatment. Individuals with indolent B-cell lymphoma have impaired antibody and cellular responses that were independent of treatment. The significant reduction and heterogeneity in immune responses in these individuals emphasise the urgent need for immune response monitoring and alternative prophylactic strategies to protect against COVID- 19.

Transmission dynamics of SARS-CoV-2 in a strictly-Orthodox Jewish community in the UK

Some social settings such as households and workplaces, have been identified as high risk for SARS-CoV-2 transmission. Identifying and quantifying the importance of these settings is critical for designing interventions. A tightly-knit religious community in the UK experienced a very large COVID-19 epidemic in 2020, reaching 64.3% seroprevalence within 10 months, and we surveyed this community both for serological status and individual-level attendance at particular settings. Using these data, and a network model of people and places represented as a stochastic graph rewriting system, we estimated the relative contribution of transmission in households, schools and religious institutions to the epidemic, and the relative risk of infection in each of these settings. All congregate settings were important for transmission, with some such as primary schools and places of worship having a higher share of transmission than others. We found that the model needed a higher general-community transmission rate for women (3.3-fold), and lower susceptibility to infection in children to recreate the observed serological data. The precise share of transmission in each place was related to assumptions about the internal structure of those places. Identification of key settings of transmission can allow public health interventions to be targeted at these locations.

Comprehensive antibody profiling of mRNA vaccination in children

While children have been largely spared from COVID-19 disease, the emergence of viral variants of concern (VOC) with increased transmissibility, combined with fluctuating mask mandates and school re-openings have led to increased infections and disease among children. Thus, there is an urgent need to roll out COVID-19 vaccines to children of all ages. However, whether children respond equivalently to adults to mRNA vaccines and whether dosing will elicit optimal immunity remains unclear. Given the recent announcement of incomplete immunity induced by the pediatric dose of the BNT162b2 vaccine in young children, here we aimed to deeply profile and compare the vaccine-induced humoral immune response in 6-11 year old children receiving the pediatric (50g) or adult (100g) dose of the mRNA-1273 vaccine compared to adults and naturally infected children or children that experienced multi inflammatory syndrome in children (MIS-C) for the first time. Children elicited an IgG dominant vaccine induced immune response, surpassing adults at a matched 100g dose, but more variable immunity at a 50g dose. Irrespective of titer, children generated antibodies with enhanced Fc-receptor binding capacity. Moreover, like adults, children generated cross-VOC humoral immunity, marked by a decline of omicron receptor binding domain-binding, but robustly preserved omicron Spike-receptor binding, with robustly preserved Fc-receptor binding capabilities, in a dose dependent manner. These data indicate that while both 50g and 100g of mRNA vaccination in children elicits robust cross-VOC antibody responses, 100ug of mRNA in children results in highly preserved omicron-specific functional humoral immunity. One-Sentence SummarymRNA vaccination elicits robust humoral immune responses to SARS-CoV-2 in children 6-11 years of age.

Antibody Responses after SARS-CoV-2 Vaccination in Lymphoma

Individuals with lymphoid malignancies have an increased mortality risk from COVID-19. Paradoxically, this population is least likely to be protected by SARS-CoV-2 vaccination as a result of disease- or treatment-related immunosuppression. Current data on vaccine responses in persons with lymphoid malignancies is limited. PROSECO is a UK multi-centre prospective observational study evaluating COVID-19 vaccine immune responses in individuals with lymphoma. This early interim analysis details the antibody responses to first- and second-SARS-CoV-2 vaccination with either BNT162b2 (Pfizer-BioNTech) and ChAdOx1 (AstraZeneca), in 129 participants. Responses are compared to those obtained in healthy volunteers. The key findings of this interim analysis are first, 61% of participants who are vaccinated during or within 6 months of receiving systemic anti-lymphoma treatment, do not have detectable antibodies despite two doses of vaccine. Second, individuals with curable disease such has Hodgkin (6/6) and aggressive B-cell non-Hodgkin lymphoma (13/16) develop robust antibody levels to either first or second doses, when vaccinated > 6 months after treatment completion. Third, participants incurable, indolent lymphomas have reduced antibody levels to first and second vaccine doses, irrespective of treatment history. Finally, whilst there was no difference in antibody responses between BNT162b2 and ChAdOx1 in lymphoma participants, BNT162b2 induces 11-fold higher antibody responses than ChAdOx1 after the second dose in healthy donors. These findings serve to reassure the community that individuals with treated Hodgkin and aggressive B-NHL can develop antibody responses to SARS-CoV-2 vaccine. Simultaneously it also highlights the critical need to identify an alternative strategy against COVID-19 for those undergoing systemic anti-lymphoma treatment, and for individuals with indolent lymphomas.

Evidence for antibody as a protective correlate for COVID-19 vaccines

Though eleven novel COVID-19 vaccines have demonstrated efficacy, additional affordable, scalable, and deliverable vaccines are needed to meet unprecedented global demand. With placebo-controlled efficacy trials becoming infeasible due to the roll out of licensed vaccines, a correlate of protection is urgently needed to provide a path for regulatory approval of novel vaccines. To assess whether antibody titers may reasonably predict efficacy, we evaluated the relationship between efficacy and in vitro neutralizing and binding antibodies of 7 vaccines for which sufficient data have been generated. Once calibrated to titers of human convalescent sera reported in each study, a robust correlation was seen between neutralizing titer and efficacy ({rho}= 0.79) and binding antibody titer and efficacy ({rho} = 0.93), despite geographically diverse study populations subject to different forces of infection and circulating variants, and use of different endpoints, assays, convalescent sera panels and manufacturing platforms. This correlation is strengthened by substituting post-hoc analyses for efficacy against the ancestral strain (D614G), where available. Together with an accumulating body of evidence from natural history studies and animal models, these results support the use of post-immunization antibody titers as the basis for establishing a correlate of protection for COVID-19 vaccines.

Extremely high SARS-CoV-2 seroprevalence in a strictly-Orthodox Jewish community in the UK

BackgroundEthnic and religious minorities have been disproportionately affected by SARS-CoV-2 worldwide. The UK strictly-Orthodox Jewish community has been severely affected by the pandemic. This group shares characteristics with other ethnic minorities including larger family sizes, higher rates of household crowding and relative socioeconomic deprivation. We studied a UK strictly-Orthodox Jewish population to understand how COVID-19 had spread within this community. MethodsWe performed a household-focused cross-sectional SARS-CoV-2 serosurvey specific to three antigen targets. Randomly-selected households completed a standardised questionnaire and underwent serological testing with a multiplex assay for SARS-CoV-2 IgG antibodies. We report clinical illness and testing before the serosurvey, seroprevalence stratified by age and gender. We used random-effects models to identify factors associated with infection and antibody titres. FindingsA total of 343 households, consisting of 1,759 individuals, were recruited. Serum was available for 1,242 participants. The overall seroprevalence for SARS-CoV-2 was 64.3% (95% CI 61.6-67.0%). The lowest seroprevalence was 27.6% in children under 5 years and rose to 73.8% in secondary school children and 74% in adults. Antibody titres were higher in symptomatic individuals and declined over time since reported COVID-19 symptoms, with the decline more marked for nucleocapsid titres. InterpretationIn this tight-knit religious minority population in the UK, we report one of the highest SARS-CoV-2 seroprevalence levels in the world to date. In the context of this high force of infection, all age groups experienced a high burden of infection. Actions to reduce the burden of disease in this and other minority populations are urgently required. FundingThis work was jointly funded by UKRI and NIHR [COV0335; MR/V027956/1], a donation from the LSHTM Alumni COVID-19 response fund, HDR UK, the MRC and the Wellcome Trust. The funders had no role in the design, conduct or analysis of the study or the decision to publish. The authors have no financial relationships with any organizations that might have an interest in the submitted work in the previous three years; no other relationships or activities that could appear to have influenced the submitted work. Research In ContextO_ST_ABSEvidence before the studyC_ST_ABSIn January 2020, we searched PubMed for articles on rates of SARS-CoV-2 infection amongst ethnic minority groups and amongst the Jewish population. Search teams included "COVID-19", "SARS-CoV-2", seroprevalence, "ethnic minority", and "Jewish" with no language restrictions. We also searched UK government documents on SARS-CoV-2 infection amongst minority groups. By January 2020, a large number of authors had reported that ethnic minority groups experienced higher numbers of cases and increased hospitalisations due to COVID-19. A small number of articles provided evidence that strictly-Orthodox Jewish populations had experienced a high rate of SARS-CoV-2 infection but extremely limited data was available on overall population level rates of infection amongst specific ethnic minority population groups. There was also extremely limited data on rates of infection amongst young children from ethnic minority groups. Added value of the studyWe report findings from a population representative, household survey of SARS-CoV-2 infection amongst a UK strictly Orthodox Jewish population. We demonstrate an extremely high seroprevalence rate of SARS-CoV-2 in this population which is more than five times the estimated seroprevalence nationally and five times the estimated seroprevalence in London. In addition the large number of children in our survey, reflective of the underlying population structure, allows us to demonstrate that in this setting there is a significant burden of disease in all age groups with secondary school aged children having an equivalent seroprevalence to adults. Implications of the available evidenceOur data provide clear evidence of the markedly disproportionate impact of SARS-CoV-2 in minority populations. In this setting infection occurs at high rates across all age groups including pre-school, primary school and secondary school-age children. Contextually appropriate measures to specifically reduce the impact of SARS-CoV-2 amongst minority populations are urgently required.

Long-Term Persistence of Spike Antibody and Predictive Modeling of Antibody Dynamics Following Infection with SARS-CoV-2

BackgroundAntibodies to Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) have been shown to neutralize the virus in-vitro. Similarly, animal challenge models suggest that neutralizing antibodies isolated from SARS-CoV-2 infected individuals prevent against disease upon re-exposure to the virus. Understanding the nature and duration of the antibody response following SARS-CoV-2 infection is therefore critically important. MethodsBetween April and October 2020 we undertook a prospective cohort study of 3555 healthcare workers in order to elucidate the duration and dynamics of antibody responses following infection with SARS-CoV-2. After a formal performance evaluation against 169 PCR confirmed cases and negative controls, the Meso-Scale Discovery assay was used to quantify in parallel, antibody titers to the SARS-CoV-2 nucleoprotein (N), spike (S) protein and the receptor-binding-domain (RBD) of the S-protein. All seropositive participants were followed up monthly for a maximum of 7 months; those participants that were symptomatic, with known dates of symptom-onset, seropositive by the MSD assay and who provided 2 or more monthly samples were included in the analysis. Survival analysis was used to determine the proportion of sero-reversion (switching from positive to negative) from the raw data. In order to predict long-term antibody dynamics, two hierarchical longitudinal Gamma models were implemented to provide predictions for the lower bound (continuous antibody decay to zero, "Gamma-decay") and upper bound (decay-to-plateau due to long lived plasma cells, "Gamma-plateau") long-term antibody titers. ResultsA total of 1163 samples were provided from 349 of 3555 recruited participants who were symptomatic, seropositive by the MSD assay, and were followed up with 2 or more monthly samples. At 200 days post symptom onset, 99% of participants had detectable S-antibody whereas only 75% of participants had detectable N-antibody. Even under our most pessimistic assumption of persistent negative exponential decay, the S-antibody was predicted to remain detectable in 95% of participants until 465 days [95% CI 370-575] after symptom onset. Under the Gamma-plateau model, the entire posterior distribution of S-antibody titers at plateau remained above the threshold for detection indefinitely. Surrogate neutralization assays demonstrated a strong positive correlation between antibody titers to the S-protein and blocking of the ACE-2 receptor in-vitro [R2=0.72, p<0.001]. By contrast, the N-antibody waned rapidly with a half-life of 60 days [95% CI 52-68]. DiscussionThis study has demonstrated persistence of the spike antibody in 99% of participants at 200 days following SARS-CoV-2 symptoms and rapid decay of the nucleoprotein antibody. Diagnostic tests or studies that rely on the N-antibody as a measure of seroprevalence must be interpreted with caution. Our lowest bound prediction for duration of the spike antibody was 465 days and our upper bound predicted spike antibody to remain indefinitely in line with the long-term seropositivity reported for SARS-CoV infection. The long-term persistence of the S-antibody, together with the strong positive correlation between the S-antibody and viral surrogate neutralization in-vitro, has important implications for the duration of functional immunity following SARS-CoV-2 infection.

Evaluation of a novel multiplexed assay for determining IgG levels and functional activity to SARS-CoV-2.

BackgroundThe emergence of SARS-CoV-2 has led to the development of new serological assays that could aid in diagnosis and evaluation of seroprevalence to inform an understanding of the burden of COVID-19 disease. Many available tests lack rigorous evaluation and therefore results may be misleading. ObjectivesThe aim of this study was to assess the performance of a novel multiplexed immunoassay for the simultaneous detection of antibodies against SARS-CoV-2 trimeric spike (S), spike receptor binding domain (RBD), spike N terminal domain and nucleocapsid antigen and a novel pseudo-neutralisation assay. MethodsA multiplexed solid-phase chemiluminescence assay (Meso Scale Discovery) was evaluated for the simultaneous detection of IgG binding to four SARS-CoV-2 antigens and the quantification of antibody-induced ACE-2 binding inhibition (pseudo-neutralisation assay). Sensitivity was evaluated with a total of 196 COVID-19 serum samples (169 confirmed PCR positive and 27 anti-nucleocapsid IgG positive) from individuals with mild symptomatic or asymptomatic disease. Specificity was evaluated with 194 control serum samples collected from adults prior to December 2019. ResultsThe specificity and sensitivity of the binding IgG assay was highest for S protein with a specificity of 97.4% and sensitivity of 96.2% for samples taken 14 days and 97.9% for samples taken 21 days following the onset of symptoms. IgG concentration to S and RBD correlated strongly with percentage inhibition measured by the pseudo-neutralisation assay. ConclusionExcellent sensitivity for IgG detection was obtained over 14 days since onset of symptoms for three SARS-CoV-2 antigens (S, RBD and N) in this multiplexed assay which can also measure antibody functionality.

Humoral Response Dynamics Following Infection with SARS-CoV-2

IntroductionSevere Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) specific antibodies have been shown to neutralize the virus in-vitro. Understanding antibody dynamics following SARS-CoV-2 infection is therefore crucial. Sensitive measurement of SARS-CoV-2 antibodies is also vital for large seroprevalence surveys which inform government policies and public health interventions. However, rapidly waning antibodies following SARS-CoV-2 infection could jeopardize the sensitivity of serological testing on which these surveys depend. MethodsThis prospective cohort study of SARS-CoV-2 humoral dynamics in a central London hospital analyzed 137 serial samples collected from 67 participants seropositive to SARS-CoV-2 by the Meso-Scale Discovery assay. Antibody titers were quantified to the SARS-CoV-2 nucleoprotein (N), spike (S-)protein and the receptor-binding-domain (RBD) of the S-protein. Titers were log-transformed and a multivariate log-linear model with time-since-infection and clinical variables was fitted by Bayesian methods. ResultsThe mean estimated half-life of the N-antibody was 52 days (95% CI 42-65). The S- and RBD-antibody had significantly longer mean half-lives of 81 days (95% CI 61-111) and 83 days (95% CI 55-137) respectively. An ACE-2-receptor competition assay demonstrated significant correlation between the S and RBD-antibody titers and ACE2-receptor blocking in-vitro. The time-to-a-negative N-antibody test for 50% of the seropositive population was predicted to be 195 days (95% CI 163-236). DiscussionAfter SARS-CoV-2 infection, the predicted half-life of N-antibody was 52 days with 50% of seropositive participants becoming seronegative to this antibody at 195 days. Widely used serological tests that depend on the N-antibody will therefore significantly underestimate the prevalence of infection following the majority of infections. Significance statementWe believe that our study has significant and urgent public health and translational impact. Firstly, our findings demonstrate that the half-life of the SARS-CoV-2 nucleoprotein antibody is only 52 days. This has immediate and important implications for large-scale seroprevalence surveys, government policy and mathematical modelling predictions which rely on serological tests that target this antibody. Secondly, the slower decay of the SARS-CoV-2 spike protein antibody identified in this study makes assays to the spike protein a more reliable target for serological assays in the longer term. We demonstrate a strong positive linear correlation between spike/RBD antibody and ACE-2 receptor binding in vitro. Our findings are therefore likely to reflect the time to loss of a functional antibody response in SARS-CoV-2. FundingGOSH charity, Wellcome Trust (201470/Z/16/Z and 220565/Z/20/Z). GOSH NIHR Funded Biomedical Research Centre. Trial registration numberNCT04380896.