Effect of daily alcohol consumption and age over 40 years on COVID-19 vaccination antibody titers in the Delta era among hospital workers in northern Okinawa, Japan: A retrospective cohort study

• COVID-19 vaccination effectively prevents infection and reduces disease severity. • Several factors, including lifestyle, affect COVID-19 vaccination antibody titers. • Vaccination interval in those aged >40 years affects COVID-19 vaccine efficacy. • Daily alcohol consumption cessation improves COVID-19 vaccine efficacy. Coronavirus disease 2019 (COVID-19) vaccination has demonstrated efficacy in preventing infection, mitigating disease severity, and lowering the incidence of Long COVID. To enhance vaccine effectiveness, it is not only important to develop more effective vaccines but also to clarify factors, including lifestyle, that affect the immune response. The aim of this study was to investigate the impact of lifestyle factors on COVID-19 vaccination antibody titers. Antibody titers of 354 hospital workers who received two COVID-19 vaccination doses were measured five times for more than six months. Information on medical history, demographic characteristics, and lifestyle-related items was obtained from hospital health checkups. The outcome variable (Lower-25 %) was defined as the antibody titer value below the 25th percentile of the fifth measurement. The Cox proportional hazard survival model was used to evaluate the hazard ratio for incidence of Lower-25 % according to lifestyle-related items. The crude incidence rates per 1,000 person-days for Lower-25 % among women and men were 1.35 and 1.66, respectively. The hazard ratios for Lower-25 % of those in their 40 s, 50 s, and 60 s compared with those in their 20 s were 5.82 (95 % confidence interval [CI], 2.05–16.51), 7.12 (95 % CI, 2.46–20.63), and 9.96 (95 % CI, 3.07–32.34), respectively. The hazard ratios for “daily” versus “never” drinking habits were 2.26 (95 % CI 1.17–4.34). The results of this study indicate that shortening vaccination intervals for individuals over 40 years and discontinuing daily alcohol consumption are associated with the preservation of acquired antibody titers for optimizing vaccine efficacy.