Influenza Sentinel Surveillance in the Post-coronavirus Disease 2019 Period

초록

To describe influenza activity in the Republic of Korea during the 2023-2024 and 2024-2025 seasons following the coronavirus disease 2019 (COVID-19) pandemic, using sentinel surveillance data, and to compare season-specific epidemiological patterns. Sentinel surveillance data on patients with influenza-like illness (ILI), those hospitalized for influenza, and influenza virological findings reported to the Korea Disease Control and Prevention Agency from week 36 of 2023 to week 35 of 2025 were analyzed. In the 2023-2024 season, influenza activity returned to pre-COVID-19 levels, with ILI peaking in week 49 of 2023 and increased hospitalizations compared with the previous season. In the 2024-2025 season, ILI reached its highest level since 2016, when a comparable surveillance system was established. In both seasons, school-aged children and adolescents (7-18 years) were the main drivers of influenza transmission, whereas hospitalizations were most common among adults aged ≥65 years. Virological surveillance confirmed the circulation of both influenza A and B viruses. Post-COVID-19 influenza patterns differed from those previously observed, likely reflecting the continued effects of immunity debt. These findings support strengthening sentinel surveillance, expanding outpatient sites to improve regional representativeness, and providing timely influenza surveillance updates to healthcare professionals and the public through weekly reports and the FluON dashboard. Copyright © Korea Disease Control and Prevention Agency.

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