Risk of Death in Older Japanese Adults with COVID-19 Caused by the Omicron Variant: a Population-Based Study

Abstract

We assessed case fatality rates (CFRs) in adults aged ≥70 years in 10 prefectures in Japan (14.8 million residents) diagnosed between January 2022 and March 2023, when the Omicron variant was dominant in Japan. We selected incident reports on 283,052 cases from participating public health centers reported according to the Infectious Diseases Control Law. Patients were passively followed up until the end of their isolation, date of death, or 28 days after COVID-19 diagnosis, whichever occurred first. We calculated age-standardized CFRs with 95% confidence intervals (CIs) using the Japanese population aged 70–79, 80–89 and ≥90 years in 2022, divided into 16 subgroups according to the period of COVID-19 diagnosis. The overall CFR was 1.59% (95% CI: 1.55–1.64%); ranging between 0.67% (95% CI: 0.38–0.96%, from May 23 to June 19, 2022) and 2.58% (95% CI: 2.36–2.80%, from January 31 to February 27, 2022). The age-standardized CFRs had three peaks, (2.2% from January 31 to February 27, 2022; 1.0% from July 18 to August 14, 2022; and 1.6% from December 26, 2022 to January 22, 2023) coinciding with the 6th, 7th, and 8th COVID-19 waves in Japan caused by the Omicron variant. Population-based CFRs for Omicron variant COVID-19 in adults aged ≥70 years remained <3% throughout the period January 2022 to March 2023, including during three large waves in Japan.