Antibody Responses and Infection Prevention following the Sixth Vaccination using the BA.1 bivalent COVID-19 vaccine among Healthcare workers during the XBB variant Dominance in Japan

The effect of antibodies elicited by bivalent mRNA vaccines (original and omicron BA.1) on preventing coronavirus disease 2019 (COVID-19) onset in the presence of the XBB variant remains unknown. A prospective cohort study conducted at Chiba University Hospital examined healthcare workers who received their sixth vaccination with the Pfizer-BioNTech COVID-19 bivalent mRNA vaccine (original and omicron BA.1). Researchers quantitatively measured serum anti-spike (S) antibody levels. Participants not infected during the 60-day observation period after vaccination had significantly higher S antibody titers than those who were newly infected (27756 U/mL, 95% CI [24988–30831 U/mL] vs. 15321 U/mL, 95% CI [10824–21688 U/mL], p