Hospitalization of mild cases of community-acquired pneumonia decreased more than severe cases during the COVID-19 pandemic

•The number of inpatient community-acquired pneumonia cases decreased in the pandemic.•The number of inpatient cases decreased according to the severity of pneumonia.•The interrupted time series analysis showed a significant inpatient case reduction. The coronavirus disease 2019 (COVID-19) pandemic has affected all healthcare systems. This study aimed to assess the impact of the COVID-19 pandemic on the number and severity of cases of community-acquired pneumonia (CAP) in Japan. Using claims data from the Quality Indicator/Improvement Project (QIP) database, urgent cases of inpatients for CAP from 01 August 2018 to 30 July 2020 were included. The monthly ratios of inpatient cases were compared from August 2018 to July 2019 and August 2019 to July 2020 as a year-over-year comparison. These ratios were also compared according to the “A-DROP” severity score, and an interrupted time series (ITS) analysis was performed to evaluate the impact of the COVID-19 pandemic on the monthly number of inpatient cases. This study included a total of 67,900 inpatient cases for CAP in 262 hospitals. During the COVID-19 pandemic (defined as the period between March and July 2020) the number of inpatient cases for CAP drastically decreased compared with the same period in the previous year (–48.1%), despite a temporary reduction in the number of other urgent admissions. The number of inpatient cases decreased according to the severity of pneumonia. Milder cases showed a greater decrease in the year-over-year ratio than severe ones: mild –55.2%, moderate –45.8%, severe –39.4%, and extremely severe –33.2%. The ITS analysis showed that the COVID-19 pandemic significantly reduced the monthly number of inpatient cases for CAP (estimated decrease: –1233 cases; 95% CI –521 to –1955). This study showed a significant reduction in the number of inpatient cases for CAP during the COVID-19 pandemic in Japan. The milder cases showed a greater decrease in the year-over-year ratio of the number of inpatient cases.