Humoral response post-BNT162b2 single booster in pre-vaccination baseline SARS-CoV-2 seronegative and seropositive subjects

Background: we report here data on humoral immune response post-BNT162b2 primary vaccination and booster in pre-vaccination baseline severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) seronegative and seropositive subjects. Methods: the study population consisted in 51 baseline SARS-CoV-2 seronegative and 11 baseline SARS-CoV-2 seropositive subjects, who underwent primary mRNA-based BNT162b2 vaccination (two doses) followed by homologous booster administration (third dose). Venous blood was sequentially collected up to 1 months after vaccine booster administration, and humoral response was monitored by measuring anti-SARS-CoV-2 spike trimeric IgG antibodies. Results: the humoral response after the three doses of BNT162b2 displayed an overlapping trend in the two groups, although the baseline and post-primary vaccination concentration of anti-SARS-CoV-2 spike trimeric IgG were constantly higher in baseline SARS-CoV-2 seropositive than in baseline SARS-CoV-2 seronegative subjects (all p<0.001). Unlike before vaccine booster administration, the levels of anti-SARS-CoV-2 spike trimeric IgG, 1 month after receiving the third BNT162b2 dose were not significantly different between pre-vaccination baseline SARS-CoV-2 seropositive and seronegative subjects (7 430 versus 9 020 kBAU/L; p=0.232). In both cohorts, all recipients of vaccine booster displayed antibodies levels >264 kBAU/L. Conclusion: the results of this study demonstrate that although baseline SARS-CoV-2 seropositive subjects have magnified humoral response to primary BNT162b2 vaccination, vaccine booster generates anti-SARS-CoV-2 spike trimeric IgG values not different from those found in baseline SARS-CoV-2 seronegative subjects. Thus, this study provides evidence that a prior SARS-CoV-2 infection does not mitigate the need for additional vaccine boosters.