Risk of death in old Japanese COVID-19 cases infected with the Omicron variant: a population-based study.

Abstract

We assessed case fatality rates (CFRs) in cases aged ≥70 years in 10 Japanese prefectures (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 study subjects from participating Public Health Centers adhering to the Infectious Diseases Control Law. Cases were passively followed up until the end of their isolation, date of death or 28 days after the COVID-19 diagnosis, whichever occurred first. We calculated age-standardized CFRs with 95% confidence intervals (CI) using the Japanese population aged 70-79, 80-89 and ≥90 in 2022 divided into 16 subgroups according to the period of COVID-19 diagnosis. The total overall CFR was 1.59% (95% CI 1.55-1.64); it ranged between 0.67% (95% CI 0.38-0.96, May 23-June 19) and 2.58% (95% CI 2.36-2.80, January 31-February 27). We observed three peaks of age-standardized CFRs paralleling the 6^th, 7^th and 8^th endemic COVID-19 waves driven by Omicron in Japan (2.2% January 31-February 27, 1.0% July 18-August 14 and 1.6% December 26-January 22, 2023, respectively). Population-based CFRs for Omicron variant COVID-19 in Japanese aged ≥70 years remained <3% throughout the period January 2022-March 2023, including during three large endemic waves in this country.