Antibody response in individuals infected with SARS-CoV-2 early after the first dose of the BNT162b2 mRNA vaccine

This study demonstrated that the titers of SARS-CoV-2 RBD-binding IgG and neutralizing antibodies induced by vaccination with BNT162b2 were significantly higher in HCWs infected with SARS-CoV-2 ≤ 14 days after the first vaccine dose than in naïve subjects, but significantly lower than in HCWs infected before vaccination. In addition, the relatively high levels of RBD-binding IgG and neutralizing antibodies in HCWs infected after vaccination were similar to those achieved after natural infection. This level of immunity probably confers protection against symptomatic SARS-CoV-2 infection and disease, according with data from the literature which showed that the levels of neutralizing antibodies detected in convalescent serum prevent severe infection.5 However, as the minimum level of antibodies associated with protection has not been defined,6 a cautionary approach is preferable. Thus, while recommending a single dose for individuals who were infected months before vaccination, the same approach might not be appropriate for those who are diagnosed with the infection soon after the first dose of vaccine, especially in the context of the emergence and spread of variants of concern which escape antibody neutralization.7 In our study, the strategy to postpone the second dose of two months in this group of HCWs allowed to rapidly achieve an optimal antibody response. This is crucial for elderly and immunosuppressed individuals (not included in our study population), since they mount significantly lower antibody responses than younger and healthy adults and are at risk of breakthrough infections.8