SARS-CoV-2 neutralizing antibodies after one or two doses of Comirnaty (BNT162b2, BioNTech/Pfizer): Kinetics and comparison with chemiluminescent assays.

BACKGROUND: Studies evaluating neutralizing antibody (NAb) after BNT162b2 vaccine are scarce. We therefore compared NAb using the plaque reduction neutralization test (PRNT) in vaccinated subjects, with those from five chemiluminescent (CLIA) assays, two targeting ACE and S-RBD interaction. METHODS: Sera from 174 completely Comirnaty/BNT162b2 vaccinated healthcare workers (HCW) were evaluated at t12 and t28. NAb titers at low (PRNT50) or high (PRNT90) stringency were compared with: Liaison SARS-CoV-2 Trimeric-S IgG, Elecsys S-RBD Ab, Maglumi SARS-CoV-2 S-RBD IgG and SARS-CoV-2 Nab; iFlash 2019-nCoV NAb. RESULTS: Neither PRNT50 nor PRNT90 correlated with age (range, 24-65 years); no significant differences were found for gender. PRNT50 and PRNT90 seropositive titers (≥1:20) were 43 (24.7%) and 15 (8.6%) at t12 and 167 (95.9%) and 149 (85.6%) at t28. CLIA results at t28 were uncorrelated with age, apart from Elecsys S-RBD Ab (r = -0.164, p = 0.046). Gender differences were found for Maglumi SARS-CoV-2 S-RBD IgG (p = 0.037) and Maglumi NAb (p = 0.046). Considering PRNT50 at thresholds of 1:20 (or 1:40) and 1:160 (or 1:320), corresponding to different immune protective levels, CLIA cut-offs have been identified. CONCLUSIONS: Comirnaty/BNT162b2 elicits strong NAb production, especially 28 days after first inoculum. Differences in correlation between Nab titers and circulating antibodies measured by 5 immunoassays have been found, being stronger the correlation for Maglumi Nab.

Antibody response to first and second dose of BNT162b2 in a cohort of characterized healthcare workers.

BACKGROUND: Vaccine-induced population immunity is a key global strategy to control coronavirus disease 2019 (COVID-19). The rapid implementation and availability of several COVID-19 vaccines is now a global health-care priority but more information about humoral responses to single- and double-dose vaccine is needed. METHODS: 163 health care workers (HCW) of the Padua University Hospitals, who underwent a complete vaccination campaign with BNT162b2 vaccine were asked to collect serum samples at 12 (t12) and 28 (t28) days after the first inoculum to allow the measurement of SARS-CoV-2 Antibodies (Ab) using chemiluminescent assays against the spike (S) protein and the Receptor Binding Domain (RBD) of the virus, respectively. RESULTS: Significant differences were found at t12 for infection-naïve and subjects with previous-natural infection who present higher values of specific antibodies, while no significant differences have been found between t12 and t28. No statistically significant difference was found between male and female, while lower Ab levels have been observed in subjects older than 60 years at t12 but not at t28. CONCLUSIONS: Our study confirms observed differences in vaccine responses between infection-naïve and subjects with previous natural infection at t12 but not for a longer time. The influence of sex and age deserves further studies, even if the relationship with age seems particularly significant.