COVID-19 Pandemic's Lasting Impact on Influenza in Finland

Strategic Insights -

A study published in the Finnish Institute for Health and Welfare found that the COVID-19 pandemic had a lasting impact on influenza in Finland. The research, conducted from 2019 to 2024, monitored influenza epidemiology in the country through national surveillance data. The findings indicate that the pandemic led to the elimination of the B/Yamagata lineage and improved vaccination coverage in the elderly population. Notably, influenza incidence was significantly reduced during the 2020/2021 season, with the virus largely absent. However, the 2021/2022 epidemic peaked exceptionally late, and activity returned to prepandemic levels in 2022/2023.

Key Takeaways:

  • The COVID-19 pandemic led to the elimination of the B/Yamagata lineage in Finland, a significant change in the country's influenza epidemiology.
  • Influenza incidence in Finland was significantly reduced during the 2020/2021 season, with the virus largely absent.
  • The 2021/2022 epidemic peaked exceptionally late, with a noticeable shift in the timing of the outbreak.
  • Influenza activity returned to prepandemic levels in 2022/2023, but the virus's impact on young children and elderly people differed.
  • The vaccine effectiveness against hospitalization due to laboratory-confirmed influenza in young children and elderly people was 68% and 42% in 2022/2023, respectively.
  • The percentage of vaccinated young children remained constant (31% to 37%), while the percentage of vaccinated elderly people increased from 48% in 2019/2020 to 63% in 2021/2022.
  • The COVID-19 pandemic had a lasting effect on the Finnish influenza surveillance system, with the need to improve participation in sentinel surveillance highlighted by the research.

Statistics:

  • The Finnish influenza surveillance system combines traditional virological surveillance and analyses of electronic health records.
  • The study monitored influenza epidemiology in Finland from 2019 to 2024, covering a population of 5.5 million.
  • Influenza incidence in Finland was evaluated based on three register-based outcomes: laboratory-confirmed infections, primary health care visits, and hospitalizations.
  • The research found that the percentage of vaccinated young children remained constant (31% to 37%), while the percentage of vaccinated elderly people increased from 48% (577,404/1,211,732) in 2019/2020 to 63% (787,771/1,255,644) in 2021/2022.
  • The vaccine effectiveness against hospitalization due to laboratory-confirmed influenza in young children and elderly people was 68% (95% confidence interval: 38%; 83%) and 42% (34%; 50%) in 2022/2023, respectively.
  • The study analyzed 717 sentinel specimens, with none testing positive for B/Yamagata.

Sources:

  • Influenza Epidemiology in Finland During and After the COVID-19 Pandemic: Surveillance Data Analysis (2019-2024). Influenza and Other Respiratory Viruses, 2025;19(6).
  • Wiley-Blackwell (www.wiley.com/; Influenza and Other Respiratory Viruses - onlinelibrary.wiley.com/journal/10.1111/(ISSN)1750-2659)
  • Finnish Institute for Health and Welfare
  • NewsRx. Finnish Institute for Health and Welfare Reports Findings in COVID-19 [Influenza Epidemiology in Finland During and After the COVID-19 Pandemic: Surveillance Data Analysis (2019-2024)]. Pediatrics Week. July 5, 2025; p 2.