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.