High but Short-lived anti-SARS-CoV2 neutralizing, IgM, IgA, and IgG levels among mRNA-vaccinees compared to naturally-infected participants

1.BackgroundWaning of protection against emerging SARS-CoV-2 variants by pre-existing antibodies elicited due to current vaccination or natural infection is a global concern. Whether this is due to waning of immunity to SARS-COV-2 remains unclear. AimWe aimed to investigate dynamics of antibody isotype responses among vaccinated naive (VN) and naturally infected (NI) individuals. MethodsWe followed up antibody levels in COVID-19 mRNA-vaccinated subjects without prior infection (VN, n=100) at two phases: phase-I (P-I) at [~]1.4 and phase-II (P-II) at [~]5.3 months. Antibody levels were compared to those of unvaccinated and naturally infected subjects (NI, n=40) at [~]1.7 (P-1) and 5.2 (P-II) months post-infection. Neutralizing antibodies (NTAb), anti-S-RBD-IgG, -IgM, and anti-S-IgA isotypes were measured. ResultsVN group produced significantly greater antibody responses (p<0.001) than NI group at P-I except for IgM. In VN group, a significant waning in antibody response was observed in all isotypes. There was about [~] a 4-fold decline in NTAb levels (p<0.001), anti-S-RBD-IgG ([~]5-folds, p<0.001), anti-S-RBD-IgM ([~]6-folds, p<0.001), and anti-S1-IgA (2-folds, p<0.001). In NI group, a significant but less steady decline was notable in NTAb ([~]1-folds, p<0.001), anti-S-RBD IgG ([~]1-fold, p=0.005), and S-RBD-IgM ([~]2-folds, p<0.001). Unlike VN group, NI group mounted a lasting anti-S1-IgA response with no significant decline. Anti-S1-IgA levels which were [~]3 folds higher in VN subjects compared to NI in P-1 (p<0.001), dropped to almost same levels, with no significant difference observed between the two groups in P-II. ConclusionWhile double dose mRNA vaccination boosted antibody levels, this "boost" was relatively short-lived in vaccinated individuals.

Validation of a novel fluorescent lateral flow assay for rapid qualitative and quantitative assessment of total anti-SARS-CoV-2 S-RBD binding antibody units (BAU) from plasma or fingerstick whole-blood of COVID-19 vaccinees

BackgroundLimited commercial LFA assays are available to provide a reliable quantitative measurement of the total binding antibody units (BAU/mL) against the receptor-binding domain of the SARS-CoV-2 spike protein (S-RBD). AimTo evaluate the performance of FinecareTM2019-nCoV S-RBD LFA and its fluorescent reader (FinecareTM-FIA Meter) against the following reference methods (i) The FDA-approved Genscript surrogate virus-neutralizing assay (sVNT), and (ii) three highly performing automated immunoassays: BioMerieux VIDAS(R)3, Ortho VITROS(R), and Mindray CL-900i(R). MethodsPlasma from 488 vaccinees were tested by all aforementioned assays. Fingerstick whole-blood samples from 156 vaccinees were also tested by FinecareTM. Results and conclusionsFinecareTM showed 100% specificity as none of the pre-pandemic samples tested positive. Equivalent FinecareTM results were observed among the samples taken from fingerstick or plasma (Pearson correlation r=0.9, p<0.0001), suggesting that fingerstick samples are sufficient to quantitate the S-RBD BAU/mL. A moderate correlation was observed between FinecareTM and sVNT (r=0.5, p<0.0001), indicating that FinecareTM can be used for rapid prediction of the neutralization antibody post-vaccination. FinecareTM BAU results showed strong correlation with VIDAS(R)3 (r=0.6, p<0.0001), and moderate correlation with VITROS(R) (r=0.5, p<0.0001), and CL-900i(R) (r=0.4, p<0.0001), suggesting that FinecareTM be used as a surrogate for the advanced automated assays to measure S-RBD BAU/mL.

Comparison of antibody immune responses between BNT162b2 and mRNA-1273 SARS-CoV-2 vaccines in naive and previously infected individuals

Two mRNA vaccines, Pfizer-BNT162b2 and Moderna-mRNA-1273, were granted the US Food and Drug Administration Emergency Use Authorization for preventing COVID-19. However, little is known about the difference in antibody responses induced by the two mRNA vaccines in naive and individuals with a previous history of infections (PI group). Therefore, we investigated the levels of anti-S-RBD total antibodies (IgM, IgA, and IgG), anti-S-RBD IgG, and anti-S-RBD IgA in these two groups 1-13 (median=6) weeks following administration of two doses of mRNA-1273 or BNT162b2 vaccines. Results showed that in naive-vaccinated group, the mRNA-1327 vaccine induces significantly higher levels of S-RBD total antibodies (3.5-fold; p<0.001), S-RBD IgG (2-fold-p<0.01), and S-IgA (2.1-fold, p<0.001) than the BNT162b2 vaccine. In the PI-vaccinated group, both vaccines produce significantly higher S-RBD total antibodies level than those of the naive-vaccinated group. The PI group produced a higher level of S-RBD IgG than the naive-BNT162b2 (p=0.05) but not more than the naive-mRNA-1273 (p=0.9) group. Interestingly, the PI-vaccinated group produced a comparable level of IgA ratio to the naive-mRNA-1273 group but significantly higher than the naive-BNT162b2 group (1.6-fold, p<0.001). Our results showed that the mRNA-1327 vaccine is more immunogenic and induces a greater antibody response than the BNT162b2 vaccine.

Are commercial antibody assays substantially underestimating SARS-CoV-2 ever infection? An analysis on a population-based sample in a high exposure setting

BackgroundPerformance of three automated commercial serological IgG-based assays was investigated for assessing SARS-CoV-2 ever (past or current) infection in a population-based sample in a high exposure setting. MethodsPCR and serological testing was performed on 394 individuals. ResultsSARS-CoV-2-IgG seroprevalence was 42.9% (95% CI 38.1%-47.8%), 40.6% (95% CI 35.9%-45.5%), and 42.4% (95% CI 37.6%-47.3%) using the CL-900i, VidasIII, and Elecsys assays, respectively. Between the three assays, overall, positive, and negative percent agreements ranged between 93.2%-95.7%, 89.3%-92.8%, and 93.8%-97.8%, respectively; Cohen kappa statistic ranged from 0.86-0.91; and 35 specimens (8.9%) showed discordant results. Among all individuals, 12.5% (95% CI 9.6%-16.1%) had current infection, as assessed by PCR. Of these, only 34.7% (95% CI 22.9%-48.7%) were seropositive by at least one assay. A total of 216 individuals (54.8%; 95% CI 49.9%-59.7%) had evidence of ever infection using antibody testing and/or PCR during or prior to this study. Of these, only 78.2%, 74.1%, and 77.3% were seropositive in the CL-900i, VidasIII, and Elecsys assays, respectively. ConclusionsAll three assays had comparable performance and excellent agreement, but missed at least 20% of individuals with past or current infection. Commercial antibody assays can substantially underestimate ever infection, more so when infection rates are high.