Influenza vaccine effectiveness against hospitalization during the 2018/2019 season among older persons aged ≥ 75 years in Japan: The LIFE-VENUS Study

Background: Older persons are recommended to receive annual influenza vaccinations due to their increased susceptibility to influenza infections and related complications. Routine assessments of influ-enza vaccine effectiveness (IVE) in older persons may help to improve vaccine development and vaccina-tion strategies, but there is a lack of consistent epidemiological data from Japan. This study aimed to evaluate IVE against hospitalization during the 2018/2019 season among older persons aged >= 75 years in Japan.Methods: This cohort study was conducted using insurance claims data and vaccination records provided by the Longevity Improvement & Fair Evidence -Vaccine Effectiveness, Networking, and Universal Safety (LIFE-VENUS) Study. The study cohort comprised older persons aged >= 75 years residing in an urban municipality in Japan. Vaccinated participants were identified through vaccination records from October 2018 to January 2019, and were matched with unvaccinated participants using a 1:1 ratio. The IVE against hospitalization was calculated as (1-hazard ratio) x 100% while adjusting for covariates such as age, sex, comorbidities, previous vaccinations, and care needs levels.Results: We analyzed 30,881 vaccinated participants matched with 30,881 unvaccinated participants. Among these, 587 (1.9%) vaccinated participants and 644 (2.1%) unvaccinated participants were hospital-ized during the 2018/2019 season. The adjusted IVE against hospitalization was estimated to be 28.9% (16.6-39.4%). Conclusions: The influenza vaccine for the 2018/2019 season showed moderate effectiveness among older persons in Japan. The LIFE-VENUS Study represents a potential platform for the continued monitor-ing of IVE among the older Japanese population.(c) 2022 Elsevier Ltd. All rights reserved.

Automated summary

This study evaluated the effectiveness of influenza vaccination against hospitalization during the 2018/2019 season among older persons aged >= 75 years in Japan, finding an estimated effectiveness of 28.9%. The results suggest that the influenza vaccine for the 2018/2019 season showed moderate effectiveness among older persons in Japan.