BackgroundTwo doses of the BNT162b2 vaccine yielded high effectiveness that wanes within several months. The third dose was effective in mounting a significant humoral and cellular immune response.. MethodsWe followed BNT162b2-vaccinated health-care workers monthly for IgG and neutralizing antibody (NeutAb) titers. Avidity, T-cell activation and microneutralization of sera against different variants of concern (VOC) were assessed for a sub-cohort. Linear mixed models were used to compare the durability of the second and third doses, and to assess if Omicron breakthrough infections were associated with waning dynamics. ResultsOverall 3972 participants with a third dose were followed, the rate of waning of IgG and NeutAb was slower after the third (1.32%/day and 1.32%/day, respectively) compared to the second (2.26%/per day and 3.34%/day) dose. Live-neutralization of Omicron VOC was lower compared to previous strains and demonstrated similar waning from 111 (95%CI:75-166) to 26 (95%CI:16-42) within 4 months. Mean T cell activity decreased from 98{+/-}5.4 T cells/106 PBMC to 59{+/-}9.3, within 3-5 months. Omicron breakthrough infections were associated with lower IgG peak (ratio of means 0.86 95%CI 0.80-0.91), and among participants over 65y with faster waning of both IgG and NeutAb (ratio of mean rates 1.40 95% CI 1.13-1.68 and 3.58 95% CI 1.92-6.67). No waining in IgG avidity was obsereved during 112 days after the 3rd dose. ConclusionThe third dose is more durable than the second dose, yet Omicron is relatively resistant to direct neutralization. The level of humoral response may predict breakthrough infections.
An important consequence of infection with a SARS-CoV-2 variant is protective humoral immunity against other variants. The basis for such cross-protection at the molecular level is incompletely understood. Here we characterized the repertoire and epitope specificity of antibodies elicited by Beta, Gamma and ancestral variant infection and assessed their cross-reactivity to these and the more recent Delta and Omicron variants. We developed a high-throughput approach to obtain immunoglobulin sequences and produce monoclonal antibodies for functional assessment from single B cells. Infection with any variant elicited similar cross-binding antibody responses exhibiting a remarkably conserved hierarchy of epitope immunodominance. Furthermore, convergent V gene usage and similar public B cell clones were elicited regardless of infecting variant. These convergent responses despite antigenic variation may represent a general immunological principle that accounts for the continued efficacy of vaccines based on a single ancestral variant.
An important, and often neglected, aspect of vaccine effectiveness is its impact on pathogen transmissibility, harboring major implications for public health policies. As viral load is a prominent factor affecting infectivity, its laboratory surrogate, qRT-PCR cycle threshold (Ct), can be used to investigate the infectivity-related component of vaccine effectiveness. While vaccine waning has previously been observed for viral load, during the Delta wave, it is yet unknown how Omicron viral load is affected by vaccination status, and whether vaccine-derived and natural infection protection are sustainable. By analyzing results of more than 460,000 individuals we show that while recent vaccination reduces Omicron viral load, its effect wanes rapidly. In contrast, a significantly slower waning rate is demonstrated for recovered COVID-19 individuals. Thus, while the vaccine is effective in decreasing morbidity and mortality, their relative minute effect on transmissibility and rapid waning call for reassessment of the scientific justification for "vaccine certificate", as it may promote false reassurance and promiscuous behavior.
BACKGROUNDFollowing the emergence of the Omicron variant of concern, we investigated immunogenicity, efficacy and safety of BNT162b2 or mRNA1273 fourth dose in an open-label, clinical intervention trial. METHODSPrimary end-points were safety and immunogenicity and secondary end-points were vaccine efficacy in preventing SARS-CoV-2 infections and COVID-19 symptomatic disease. The two intervention arms were compared to a matched control group. Eligible participants were healthcare-workers (HCW) vaccinated with three BNT162b2 doses, and whose IgG antibody levels were [≤]700 BAU (40-percentile). IgG and neutralizing titers, direct neutralization of live VOCs, and T-cell activation were assessed. All participants were actively screened for SARS-CoV-2 infections on a weekly basis. RESULTSOf 1050 eligible HCW, 154 and 120 were enrolled to receive BNT162b2 and mRNA1273, respectively, and compared to 426 age-matched controls. Recipients of both vaccine types had a [~]9-10-fold increase in IgG and neutralizing titers within 2 weeks of vaccination and an 8-fold increase in live Omicron VOC neutralization, restoring titers to those measured after the third vaccine dose. Breakthrough infections were common, mostly very mild, yet, with high viral loads. Vaccine efficacy against infection was 30% (95%CI:-9% to 55%) and 11% (95%CI:-43% to +43%) for BNT162b2 and mRNA1273, respectively. Local and systemic adverse reactions were reported in 80% and 40%, respectively. CONCLUSIONSThe fourth COVID-19 mRNA dose restores antibody titers to peak post-third dose titers. Low efficacy in preventing mild or asymptomatic Omicron infections and the infectious potential of breakthrough cases raise the urgency of next generation vaccine development. Trial registration numberclicaltrials.gov: NCT05231005, NCT05230953
In a prospective cohort study involving 12,413 Health Care Workers (HCW), we assessed immunogenicity, vaccine-effectiveness (VE) and safety of the third BNT162b2 vaccine dose. One month after third dose, anti-RBD-IgG were induced 1.7-folds compared to one month after the second. A significant increase in avidity from 61.1% (95%CI:56.1-66.7) to 96.3% (95%CI:94.2-98.5) resulted in a 6.1-folds neutralizing antibodies induction. Linear mixed model demonstrated that the third dose elicited a greater response among HCW[≥]60 or those with [≥]two comorbidities who had a lower response following the second dose. VE of the third dose relative to two doses was 85.6% (95% CI, 79.2-90.1%). No serious adverse effects were reported. These results suggest that the third dose is superior to the second dose in both quantity and quality of IgG-antibodies and safely boosts protection from SARS-CoV-2 infection by generating high avidity antibodies to levels that are not significantly different between healthy and vulnerable populations.
The COVID-19 pandemic raises the need for diverse diagnostic approaches to rapidly detect different stages of viral infection. The flexible and quantitative nature of single-molecule imaging technology renders it optimal for development of new diagnostic tools. Here we present a proof-of-concept for a single-molecule based, enzyme-free assay for detection of SARS-CoV-2. The unified platform we developed allows direct detection of the viral genetic material from patients samples, as well as their immune response consisting of IgG and IgM antibodies. Thus, it establishes a platform for diagnostics of COVID-19, which could also be adjusted to diagnose additional pathogens.
Public health experts emphasize the need for quick, point-of-care SARS-CoV-2 detection as an effective strategy for controlling virus spread. To this end, many "antigen" detection devices were developed and commercialized. These devices are mostly based on detecting SARS-CoV-2s nucleocapsid protein. Recently, alerts issued by both the FDA and the CDC raised concerns regarding the devices tendency to exhibit false positive results. In this work we developed a novel alternative spike-based antigen assay, comprised of four high-affinity, specific monoclonal antibodies, directed against different epitopes on the spikes S1 subunit. The assays performance was evaluated for COVID-19 detection from nasopharyngeal swabs, compared to an in-house nucleocapsid-based assay, composed of antibodies directed against the nucleocapsid. Detection of COVID-19 was carried out in a cohort of 284 qRT-PCR positive and negative nasopharyngeal swab samples. The time resolved fluorescence (TRF) ELISA spike-assay displayed very high specificity (99%) accompanied with a somewhat lower sensitivity (66% for Ct<25), compared to the nucleocapsid ELISA assay which was more sensitive (85% for Ct<25) while less specific (87% specificity). Despite being out-performed by qRT-PCR, we suggest that there is room for such tests in the clinical setting, as cheap and rapid pre-screening tools. Our results further suggest that when applying antigen detection, one must consider its intended application (sensitivity vs specificity), taking into consideration that the nucleocapsid might not be the optimal target. In this regard, we propose that a combination of both antigens might contribute to the validity of the results. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=122 SRC="FIGDIR/small/21253148v1_ufig1.gif" ALT="Figure 1"> View larger version (24K): org.highwire.dtl.DTLVardef@2cdc04org.highwire.dtl.DTLVardef@12090daorg.highwire.dtl.DTLVardef@10603dforg.highwire.dtl.DTLVardef@1e84cfa_HPS_FORMAT_FIGEXP M_FIG C_FIG Graphic abstractSchematic representation of sample collection and analysis. The figure was created using BioRender.com
BackgroundSeveral uses of Antigen rapid diagnostic tests (Ag-RDT) have been suggested. Analytical studies reported high specificity yet with lower sensitivity for detecting SARS-CoV-2 compared to qRT-PCR. Here, we present the use of these tests as a decision support tool in several settings. MethodsSamples were collected for both Ag-RDT and qRT-PCR in three different clinical settings; 1. Symptomatic patients presenting at the Emergency Departments 2. Asymptomatic patients screened upon hospitalization and 3. Health-care workers (HCW) following SARS-CoV-2 exposure. Positive percent agreement (PPA), negative percent agreement (NPA), positive predictive value (PPV) and negative predictive value (NPV) were calculated. To estimate the association between Ct value, Ag-RDT and the number of days since SARS-CoV-2 exposure or symptomatic COVID-19, a mixed model was applied. ResultsA total of 5172 samples were obtained from 4595 individuals, with Ag-RDT and qRT-PCR results. Of these, 485 samples were positive by qRT-PCR. The PPA of Ag-RDT was greater for lower Ct values, reaching 93% in cases where Ct value was lower than 25 and 85% where Ct value was lower than 30. PPA was similar between symptomatic and asymptomatic individuals. The NPV and PPV were 96.8% and 99.1%, respectively. We observed a significant correlation between Ct value and time from infection onset (p<0.001). Lower Ct values were significantly associated with a positive Ag-RDT (p=0.01). ConclusionsAg-RDT can be used as a decision support tool in various clinical settings and play a major role in early detection of SARS-CoV-2 infected individuals, highly specific and with high sensitivity to the infectious stage of disease, whether symptomatic or asymptomatic.
Full genome sequences are increasingly used to track the geographic spread and transmission dynamics of viral pathogens. Here, with a focus on Israel, we sequenced 212 SARS-CoV-2 sequences and use them to perform a comprehensive analysis to trace the origins and spread of the virus. A phylogenetic analysis including thousands of globally sampled sequences allowed us to infer multiple independent introductions into Israel, followed by local transmission. Returning travelers from the U.S. contributed dramatically more to viral spread relative to their proportion in incoming infected travelers. Using phylodynamic analysis, we estimated that the basic reproduction number of the virus was initially around ~2.0-2.6, dropping by two-thirds following the implementation of social distancing measures. A comparison between reported and model-estimated case numbers indicated high levels of transmission heterogeneity in SARS-CoV-2 spread, with between 1-10% of infected individuals resulting in 80% of secondary infections. Overall, our findings underscore the ability of this virus to efficiently transmit between and within countries, as well as demonstrate the effectiveness of social distancing measures for reducing its spread.
