| Summary: | We aimed to investigate neutralizing antibody titers (NtAbT) to the P.1 and B.1 SARS-CoV-2 variants in a cohort of healthy health care workers (HCW), including 20 previously infected individuals tested at baseline (BL<sub>inf</sub>, after a median of 298 days from diagnosis) and 21 days after receiving one vaccine dose (D1<sub>inf</sub>) and 15 uninfected subjects tested 21 days after the second-dose vaccination (D2<sub>uninf</sub>). All the subjects received BNT162b2 vaccination. D1<sub>inf</sub> NtAbT increased significantly with respect to BL<sub>inf</sub> against both B.1 and P.1 variants, with a fold-change significantly higher for P.1. D1<sub>inf</sub> NtAbT were significantly higher than D2<sub>uninf</sub> NtAbT, against B.1 and P.1. NtAbT against the two strains were highly correlated. P.1 NtAbT were significantly higher than B.1 NtAbT. This difference was significant for post-vaccination sera in infected and uninfected subjects. A single-dose BNT162b2 vaccination substantially boosted the NtAb response to both variants in the previously infected subjects. NtAb titers to B.1 and P.1 lineages were highly correlated, suggesting substantial cross-neutralization. Higher titers to the P.1 than to the B.1 strain were driven by the post-vaccination titers, highlighting that cross-neutralization can be enhanced by vaccination.
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