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. Findings: 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 comparator 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 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). Interpretation: These findings underscore the need for continued prevention and treatment of COVID-19 to prevent severe disease. Funding: Pfizer Inc. ### Competing Interest Statement KMA, MAB, KTogo, KTanabe, DC, VW, LJM, BI and SI are employees of Pfizer Inc. and/or Pfizer Japan may hold stock and/or stock options of Pfizer inc. BC, MK and YD are employees of Genesis Research, which has received consulting fees from Pfizer Inc. ### Funding Statement This study was funded by Pfizer Inc. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: This study used anonymized data that were exempted from institutional review board review by the Sterling Institutional Review Board. I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes Under Pfizer's data use agreement with Medical Data Vision, these data cannot be shared. Requests for programming software code that do not reduce the confidentiality of the data and are deemed reasonable by the study team will be considered.