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.

Performance evaluation of novel fluorescent-based lateral immune flow assay (LIFA) for rapid detection and quantitation of total anti-SARS-CoV-2 S-RBD binding antibodies in infected individuals

1.BackgroundThe vast majority of the commercially available LFIA is used to detect SARS-CoV-2 antibodies qualitatively. Recently, a novel fluorescence-based LIFA test was developed for 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 the fluorescence LIFA Finecare 2019-nCoV S-RBD test along with its reader (Model No.: FS-113). MethodsPlasma from 150 RT-PCR confirmed-positive individuals and 100 pre-pandemic samples were tested by FinCare to access sensitivity and specificity. For qualitative and quantitative validation of the FinCar measurements, the BAU/mL results of FinCare were compared with results of two reference assays: the surrogate virus-neutralizing test (sVNT, GenScript, USA), and the VIDAS(R)3 automated assay (BioMerieux, France). ResultsFinecare showed 92% sensitivity and 100% specificity compared to PCR. Cohens Kappa statistic denoted moderate and excellent agreement with sVNT and VIDAS(R)3, ranging from 0.557 (95% CI: 0.32-0.78) to 0.731 (95% CI: 0.51-0.95), respectively. A strong correlation was observed between Finecare/sVNT (r=0.7, p<0.0001) and Finecare/VIDAS(R)3 (r=0.8, p<0.0001). ConclusionFinecare is a reliable assay and can be used as a surrogate to assess binding and neutralizing antibody response post-infection or vaccination, particularly in none or small laboratory settings.

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.

Effect of multiple freeze-thaw cycles on detection of anti-SARS-CoV-2 IgG antibodies

Several studies have investigated the effect of repeated freeze-thaw (F/T) cycles on RNA detection for SARS-CoV-2. However, no data is available regarding the effect of repeated F/T cycles on SARS-CoV-2 antibody detection in serum. We investigated the effect of multiple F/T cycles on anti-SARS-CoV-2 IgG detection using an ELISA test targeting the nucleocapsid antibodies. Ten positive and one negative SARS-CoV-2 IgG sera from 11 participants, in replicates of five were subjected to a total of 16 F/T cycles and stored at 4{degrees}C until tested by ELISA. Statistical analysis was done to test for F/T cycle effect. Non-of the 10 positive sera turned into negative after 16 F/T cycles. There was no significant difference in the OD average reading between the first and last F/T cycles, except for one serum with a minimal decline in the OD. The random-effect linear regression of log (OD) on the number of cycles showed no significant trend with a slope consistent with zero (B=-0.0001; 95% CI -0.0008; 0.0006; p-value=0.781). These results suggest that multiple F/T cycles had no effect on the ability of the ELISA assay to detect the SARS-CoV-2 IgG antibodies.