Epidemiological characteristics of influenza outbreaks in schools in Jiangsu Province, China, 2020-2023 post-COVID-19 pandemic

Background: This study aimed to analyze the epidemic characteristics and influencing factors of school influenza outbreaks in Jiangsu Province, China from 2020 to 2023,following the COVID-19 pandemic, to inform prevention and control strategies.

Methods: Data on influenza-like illness(ILI) outbreaks from the Chinese Influenza Surveillance Information System and national-level influenza surveillance sentinel hospitals were analyzed. The temporal distribution, school type, virus strains, and outbreak scales were examined using descriptive statistics.

Results: From 2020 to 2023, 1142 influenza outbreaks occurred in schools, with primary schools(ages 6 to 12) accounting for 71.80%. Most large outbreaks were caused by A(H1N1) and A(H3N2), responsible for 8.99% of total outbreaks. Outbreaks were predominantly reported in the pre-peak periods of B(Victoria) and A(H1N1) circulation, accounting for 86.31% and 92.32% of their respective total outbreaks. No concurrent influenza and COVID-19 outbreaks were observed during the study period.

Conclusion: Primary and secondary schools are high-risk settings for influenza outbreaks. A(H3N2) shows higher adaptability and is more likely to co-circulate with other subtypes/lineages, especially A(H1N1), leading to larger outbreaks. B(Victoria)-caused outbreaks are more frequent but smaller in scale. School influenza outbreaks are more likely to occur during the early stages of seasonal peaks, particularly for B(Victoria) and A(H1N1). This suggests that influenza outbreaks in schools may play a crucial role in seeding and accelerating the spread of the virus within the broader community.