Influenza Vaccine Effectiveness Declines with Age in Large Japanese Cohort

Strategic Insights -

A large-scale prospective multicenter cohort study conducted annually by the Japan Physicians Association has shown that the effectiveness of influenza vaccine declines with age in a significant manner. The study, which included 148,108 patients from 543 facilities across Japan over 17 seasons, demonstrated that vaccine effectiveness was significantly lower in older adults. According to the research, this decline in effectiveness underscores the need for improved vaccines and targeted strategies for older adults.

Key Takeaways:

  • The study analyzed 148,108 patients from 543 facilities across Japan over 17 seasons, from 2002-2003 to 2018-2019.
  • The researchers found that vaccine effectiveness declined with age, with significant protection in children aged 15 and adults, but lower effectiveness in older adults.
  • The study used unadjusted and adjusted logistic regression to estimate vaccine effectiveness, with adjusted analyses showing significant protection in some age groups.
  • The research concluded that effectiveness declined with age, underscoring the need for improved vaccines and targeted strategies for older adults.
  • The study was conducted by the Japan Physicians Association and included a large sample size from across Japan.

Statistics:

  • 148,108 patients were included in the analysis.
  • 543 facilities across Japan were involved in the study.
  • 17 seasons were analyzed, from 2002-2003 to 2018-2019.
  • The study showed significant protection in children aged 15 and adults, but lower effectiveness in older adults.
  • The adjusted analyses showed significant protection in some age groups, but reduced effectiveness in older adults.

Sources:

  • Influenza vaccine effectiveness over 17 seasons in a large Japanese cohort: Analyses by age, virus type, underlying diseases and seasons before the COVID-19 pandemic. Journal of Infection and Public Health, 2025;18(11):102934.
  • NewsRx. New COVID-19 Findings Has Been Reported by Naoki Kawai et al (Influenza vaccine effectiveness over 17 seasons in a large Japanese cohort: Analyses by age, virus type, underlying diseases and seasons before the COVID-19 pandemic). Medical Letter on the CDC & FDA. September 21, 2025; p 143.