Objective  To analyze the epidemiological characteristics of influenza in Foshan, Guangdong province, from 2017 to 2022, and assess the impact of non-pharmaceutical intervention (NPI) on the incidence trend of influenza during 2020–2022 compared with 2017–2019 and provide evidence for the local prevention and control of influenza.

Methods The reported influenza case count, influenza-like illness (ILI) surveillance data, and etiological surveillance data in Foshan from 2017 to 2022 were collected through the information system of Chinese Center for Disease Control and Prevention and the influenza sentinel surveillance network in Foshan. A multidimensional comparative analysis was conducted to evaluate the epidemiological and etiological characteristics of influenza and their changes before and during the implementation of NPI.

Results From 2017 to 2022, the reported influenza cases, ILI cases, and influenza virus detections in Foshan first increased, then decreased and increased against, with significant drops observed in 2020. The data from three sources showed a positive correlarion, indicating that the annual incidence paek of influenza occurred in winter (December to January) and sub-peak occurred in summer (June to July). Significant differences were observed in annual incidence rate, ILI percentage (ILI%), and influenza virus positive rate among five districts of Foshan. Both the incidence data of influenza and ILI surveillance data revealed that the majority of cases occurred in individuals under 15 years of age, the incidence decreased with age. However, the etiological surveillance showed the highest positive rate in the 5-year-old group, followed by the 15-year-old group. All the data indicated a higher incidence in men, and the top three affected populations were students (34.53%), living scatteredly children (27.16%), and children in child care settings (15.90%). Comparative analysis on the pre-NPI period (2017–2019) and the NPI period (2020–2022) showed that the influenza incidence rate was higher during 2017-2019 (186.88/100 000) than during 2020-2022 (117.98/100 000). The ILI% was slightly higher during 2017-2019 (4.73%) compared to the adjusted ILI% during 2020-2022 (4.72%). The influenza virus positive rate decreased from 19.27% during 2017-2019 to 9.12% during 2020-2022, with the predominant subtypes shifting from A (H3N2) and A (H1N1)pdm09 to A (H3N2) and B Victoria lineage.

Conclusion From 2017 to 2022, the incidence of influenza exhibited distinct winter and summer peaks in Foshan, with children under 15 years of age being mostly affected. The implementation of NPI was associated with reduced influenza incidence, lower influenza virus positive rates, and shift of predominant influenza strains, indicating that these measures could effectively reduce the intensity of influenza transmission. Discrepancies among the three types of surveillance data highlight the necessity of integrating multiple data sources for a comprehensive analysis on influenza epidemiology.