Inpatient Burden of COVID-19 in Japan: A Retrospective Cohort Study.

Background: Changing disease dynamics and access to COVID-19 vaccines in Japan warrant a timely description of the burden of severe disease. Here we report inpatient healthcare resource utilization of COVID-19 in Japan and contextualize results with influenza.

Methods: We selected persons hospitalized for COVID-19 (ICD-10 code U07.1) from April 1, 2020 - January 31, 2024 or influenza (ICD-10 code J09.X - J11.x) from November 1, 2017 - October 31, 2019 from Medical Data Vision, a large hospital-based database in Japan. Outcomes of interest were length of stay, intensive care unit (ICU) admission, receipt of invasive mechanical ventilation (IMV), and inpatient mortality, assessed overall, as well as stratified by age groups and calendar time.

Results: Among 5,684 hospitalized COVID-19 cases, persons were older (median age 80 vs 64) and had a longer length of stay (median 21 vs 5 days) than the 18,584 influenza cases. The proportions of patients admitted to ICU (3% vs 1%), received IMV (6% vs 3%) and died in hospital (12% vs 3%) were higher in COVID-19 patients than influenza patients. Burden was higher in adult COVID-19 patients than pediatric COVID-19 patients, although for both adults and pediatric patients, COVID-19 burden surpassed influenza. Inpatient burden of COVID-19 between May 2023 and January 2024 remained greater than influenza, with 5-times longer length of stay, more frequent need for ICU care (3-times higher), IMV support (2-times higher) and in-hospital deaths (4-times higher).

Conclusions: These findings underscore the need for continued prevention and treatment of COVID-19 to prevent severe disease.