Background: Vaccine-induced population immunity is a key global strategy to control coronavirus disease 2019 (COVID-19). The rapid implementation and availability of several COVID-19 vaccines is now a global health-care priority but more information about humoral responses to single- and double-dose vaccine is needed

Methods: 163 health care workers (HCW) of the Padua University Hospitals, who underwent a complete vaccination campaign with BNT162b2 vaccine were asked to collect serum samples at 12 (t12) and 28 (t28) days after the first inoculum to allow the measurement of SARS-CoV-2 Antibodies (Ab) using chemiluminescent assays against the spike (S) protein and the Receptor Binding Domain (RBD) of the virus, respectively .

Results: Significant differences were found at t12 for infection-naive and subjects with previous-natural infection who present higher values of specific antibodies, while no significant differences have been found between t12 and t28 . No statistically significant difference was found between male and female, while lower Ab levels have been observed in subjects older than 60 years at t12 but not at t28 .

Conclusions: Our study confirms observed differences in vaccine responses between infection-naive and subjects with previous natural infection at t12 but not for a longer time . The influence of sex and age deserves further studies, even if the relationship with age seems particularly significant.