Neutralizing Antibodies Response against SARS-CoV-2 Variants of Concern Elicited by Prior Infection or mRNA BNT162b2 Vaccination

In order to determine the humoral protective response against SARS-CoV-2, the vaccine-induced and naturally induced neutralizing antibodies (NtAbs) responses against SARS-CoV-2 variants circulating in Italy through in vitro live virus neutralization assay were evaluated. A total of 39 SARS-CoV-2 recovered subjects (COVID-19+) and 63 subjects with a two-dose cycle of the BNT16262 vaccine were enrolled. A single serum sample was tested for COVID-19+ at 35–52 days post-positive swab, while vaccinees blood samples were taken at one (V1) and at three months (V3) after administration of the second vaccine dose. Significantly higher NtAb titers were found against B.1 and Alpha in both COVID-19+ and vaccinees, while lower NtAb titers were detected against Delta, Gamma, and Omicron variants. A comparison between groups showed that NtAb titers were significantly higher in both V1 and V3 than in COVID-19+, except against the Omicron variant where no significant difference was found. COVID-19+ showed lower neutralizing titers against all viral variants when compared to the vaccinees. Two-dose vaccination induced a sustained antibody response against each analyzed variant, except for Omicron. The evolution process of SARS-CoV-2, through variants originating from an accumulation of mutations, can erode the neutralizing effectiveness of natural and vaccine-elicited immunity. Therefore, a need for new vaccines should be evaluated to contain the ongoing pandemic.