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COVID-19 vaccine effectiveness against death in Japan remains unknown. Furthermore, although evidence indicates that healthcare capacity influences case-fatality risk (CFR), it remains unknown whether this relationship is mediated by age. With a modeling study, we analyzed daily COVID-19 cases and deaths during January–August 2021 by using Tokyo surveillance data to jointly estimate COVID-19 vaccine effectiveness against death and age-specific CFR. We also examined daily healthcare operations to determine the association between healthcare burden and age-specific CFR. Among fully vaccinated patients, vaccine effectiveness against death was 88.6% among patients 60–69 years of age, 83.9% among patients 70–79 years of age, 83.5% among patients 80–89 years of age, and 77.7% among patients >90 years of age. A positive association of several indicators of healthcare burden with CFR among patients >70 years of age suggested an age-dependent effect of healthcare burden on CFR in Japan.

The article discusses research on age-dependent effects of COVID-19 vaccine and effect of healthcare burden on COVID-19 deaths in Tokyo, Japan from January 1 to August 31, 2021. The study estimated COVID-19 vaccine effectiveness (VE) against death and time-varying case-fatality risk (CFR) in SARS-CoV-2-positive persons according to age group using data published by the Tokyo Metropolitan Government. Research results compare the effect of healthcare burden on CFR in older and younger age groups.