Analysis of the incidence of influenza before and after the COVID‐19 pandemic in South Korea.

Objectives: Influenza outbreaks of varying size occur every year, but during the COVID‐19 pandemic, many countries experienced influenza at lower levels. However, following the relaxation of COVID‐19 prevention measures in 2022, the incidence of influenza began to increase gradually. Thus, this study compared the occurrence of influenza from week 36 of 2017, before the COVID‐19 outbreak, until 2023. Methods: The analysis was conducted using influenza‐like illness occurrence data available from the Korea Disease Control and Prevention Agency infectious disease website. Additionally, to examine the changes in COVID‐19 and influenza occurrence during the pandemic, COVID‐19 incidence data from 20 January 2020 to 31 August 2023 were obtained from the KDCA Coronavirus Disease 19 homepage. Results: During the COVID‐19 pandemic, which corresponds to the 2020/2021 and 2021/2022 influenza seasons, there was no seasonal influenza epidemic, and the incidence rates were below the usual outbreak levels. However, in the 2022/2023 season, when the spread of COVID‐19 had eased, a seasonal pattern similar to that observed before the COVID‐19 pandemic was noted. Furthermore, correlation analysis between the rates of influenza‐like illness and COVID‐19 incidence showed no significant correlation during the entire period. However, a significant correlation emerged in 2023 (r = 0.393, p <0.05). These results suggest that influenza was suppressed during the COVID‐19 pandemic but returned to typical seasonal patterns after the COVID‐19 prevention policies were eased. Conclusion: The positive correlation observed between the incidences of COVID‐19 and influenza in 2023 indicates that COVID‐19, no longer a novel pandemic‐causing infectious disease, may have transitioned to an endemic pattern similar to seasonal influenza. [ABSTRACT FROM AUTHOR]