Antibody levels after BNT162b2 vaccine booster and SARS-CoV-2 Omicron infection

•After booster vaccination antibody levels increase after 30 days with values much higher than first and second vaccination.•After 60 and 90 days after booster dose, antibody levels decrease, suggesting the need of fourth dose.•Compared with seronegative HCWs, a higher value was observed in HCWs infected by COVID-19 before vaccination, at all dosing times, because the values are the result of natural immunity along with induced by vaccination.•14.7% of HCWs contracted Omicron virus variant, however none of these showed severe symptoms.