Epidemiological Characteristics of Influenza Outbreaks in Schools in Jiangsu Province, China, 2020- 2023 Post-COVID-19 Pandemic

Abstract

Abstract Background To understand the epidemic characteristics and influencing factors of school influenza outbreaks after the COVID-19 pandemic in Jiangsu Province, China from 2020 to 2023, and provide scientific basis for the prevention and control of school influenza. Methods We collected data on influenza-like illness(ILI) outbreaks reported in the Chinese Influenza Surveillance Information System and monitoring data from national-level influenza surveillance sentinel hospitals. Descriptive statistical analysis was conducted on the temporal distribution, school type distribution, virus strain distribution, and epidemic scale of school influenza outbreaks. Results From 2020 to 2023, a total of 833 influenza outbreaks occurred in schools in Jiangsu Province. The most reported school type was primary schools, catering to the age group of 6–12 years, accounting for 70.11% of the total reports. This study included three complete influenza seasons, with the majority of large-scale outbreaks caused by A(H1N1) and A(H3N2), accounting for 9.09% of the total outbreaks caused by them,. Outbreaks occurring in the early stages of the B(Victoria) and A(H1N1) influenza peaks accounted for 86.31% and 97.30%, respectively. The current surveillance data has not yet observed a concurrent outbreak of influenza and COVID-19. Conclusion Primary and secondary schools are high-risk locations for influenza outbreaks. The higher environmental adaptability of A(H3N2) makes it more prone to co-circulate with other subtypes/lineages, especially during concurrent circulation with A(H1N1), increasing the likelihood of large-scale outbreaks. In contrast, outbreaks caused by B (Victoria) show a higher frequency and relatively smaller scale compared to those triggered by influenza A. School influenza outbreaks are more likely to occur in the early stages of seasonal epidemics, indirectly indicating that the occurrence of influenza in schools plays a crucial role in driving the onset and development of influenza within the broader community/population. In the post-COVID-19 pandemic period, it is essential to prioritize influenza monitoring and take measures early to reduce the occurrence of outbreaks.