Influenza Epidemiology in Finland During and After the COVID‐19 Pandemic: Surveillance Data Analysis (2019–2024)
PMCID: PMC12174475
PMID: 40528677
DOI: 10.1111/irv.70131
Journal: Influenza and other respiratory viruses
Publication Date: 2025-6-17
Authors: Baum U, Ikonen N, Luomala O, Poukka E, Leino T, et al.
Key Points
- COVID-19 containment measures effectively suppressed influenza transmission, creating a unique epidemiological "natural experiment"
- Vaccine effectiveness against influenza hospitalization was 68% in young children and 42% in elderly populations in 2022-2023
- Pandemic-induced changes in healthcare surveillance and public health awareness may have long-lasting implications for respiratory disease monitoring
Summary
This comprehensive Finnish national surveillance study examined influenza epidemiology during and after the COVID-19 pandemic from 2019-2024, revealing significant disruptions to typical influenza transmission patterns. The research tracked laboratory-confirmed infections, healthcare visits, and hospitalizations across different population cohorts, with a particular focus on vaccination coverage and effectiveness among children under 6 and adults over 65.
The COVID-19 pandemic dramatically altered influenza dynamics, essentially eliminating the B/Yamagata lineage and causing unprecedented reductions in influenza activity. Notably, the 2020-2021 season saw virtually no influenza circulation, while subsequent seasons showed gradual return to prepandemic patterns. Vaccine effectiveness remained moderate, with hospitalization prevention ranging from 42-68% across age groups, and vaccination coverage among elderly populations increasing from 48% to 63% during the pandemic period.