Lessons learned from Okinawa, Japan underscore the importance of clinical epidemiology in COVID-19 prevention and control

BACKGROUND: This letter highlights the importance of clinical epidemiology in COVID-19 prevention and control, based on experiences at a core hospital in northern Okinawa, Japan, and relevant literature. METHODS: Using data from 5,097 COVID-19 patients, we conducted: (1) a descriptive cross-sectional study analyzing cases by person, time, and place; (2) an analytical cross-sectional study linking health checkup data to identify factors associated with severity (published in Environmental Health and Preventive Medicine); and (3) a cohort study of healthcare workers exploring determinants of post-vaccination antibody titers (published in Journal of Clinical Virology Plus). RESULTS: The descriptive study showed cases rose from 70 in 2020 to 891 in 2021 and 3,995 in 2022, before declining to 141 in 2023. In the analytical cross-sectional study (n = 1,353), protective factors against severity included vaccination (odds ratio [OR] [2 doses vs. 0 or one doses]: 0.223, 95% confidence interval [CI] 0.114-0.436; OR [≥3 doses vs. 0 or one doses]: 0.090, 95% CI 0.035-0.229) and regular exercise (OR ["yes" vs. "no"]: 0.458, 95% CI 0.242-0.866). In the cohort study (n = 354), lower antibody titers (lowest quartile) were more likely among older adults (hazard ratio [HR] 5.82 for 40s vs. 20s, 95% CI 2.05-16.51; HR 9.96 for 60s vs. 20s, 95% CI 3.07-32.34) and drinking habits (HR 2.26 for "daily" vs. "never", 95% CI 1.17-4.34). CONCLUSION: These findings, supported by related literature, demonstrate that clinical epidemiology played vital roles in monitoring infection trends, evaluating diagnostic and preventive measures, establishing treatment strategies, optimizing healthcare resources, and guiding policy. Its continued application will be essential for preparedness against future emerging infectious diseases.