Effectiveness of seasonal influenza vaccine in adult Japanese workers, 2017-2020

Background: Previous studies have not estimated vaccine effectiveness (VE) against influenza in the working-age Japanese population. In this study, we determined VE in adult workers at a Japanese company. Methods: We estimated VE based on self-reported data regarding influenza infections and vaccinations in employees of an auto parts manufacturing company during three influenza seasons from 2017 to 2020. VE was estimated as 100% x [1 odds ratio (the ratio of the odds of being diagnosed with influenza among enrollees with and without influenza vaccination)]. Odds ratios were estimated using logistic regression. Results: We included 11,347 worker records [3,592 (2017-18), 3,663 (2018-19), and 4,092 (2019-20)] from employees who had worked with the company throughout each influenza season. The adjusted VE was moderate and significant in the 2019-20 season (VE = 53%; 95% confidence interval [CI] = 30% to 69%) but low or negative and non-significant during the 2017-18 (VE = 28%; 95% CI =-5% to 50%) and 2018-19 (VE =-11%; 95% CI = 42% to 14%) seasons. Conclusions: Influenza vaccines were moderately effective during the 2019-20 season but showed low or negative effectiveness during the 2017-18 and 2018-19 seasons. Self-reports from worker records can successfully help determine VE against influenza. (c) 2021 Elsevier Ltd. All rights reserved.

Automated summary

This study estimated the vaccine effectiveness against influenza in adult workers at a Japanese company. The results showed that the vaccine had a moderate and significant effectiveness in the 2019-20 season, but low or negative effectiveness in the 2017-18 and 2018-19 seasons. Self-reported data from worker records can be useful in determining vaccine effectiveness against influenza.