Durability of effectiveness of a booster dose of COVID-19 bivalent (ancestral/BA.4-5) vaccine against all-cause mortality in older adults in Japan, October 2022 to September 2023

This population-based cohort study evaluated the durability of COVID-19 bivalent (ancestral/BA.4-5) booster vaccine effectiveness (VE) in Japanese residents aged ≥60 years against all-cause mortality. From October 2022 to September 2023, the all-cause mortality rate in those who had received a third booster dose with bivalent vaccine (n = 30,557) was compared with those who had received two booster doses of monovalent vaccine (n = 34,075) using Cox regression. The adjusted relative VE (95 % confidence interval) was 80 % (73 % to 85 %) 15-90 days after vaccination, 69 % (57 % to 77 %) 91-180 days after vaccination, and 31 % (-3 % to 53 %) 181-270 days after vaccination. Between April and September 2023, the relative VE (95 % confidence interval) was 62 % (44 % to 74 %) 91-180 days after vaccination. The COVID-19 bivalent booster vaccine was effective for at least 180 days after vaccination, both before and during the SARS-CoV-2 Omicron XBB-dominant period.