Epidemiological characteristics of influenza after COVID-19 pandemic in Zhejiang province, China

To analyse the epidemiological characteristics and variation trend of influenza in Zhejiang Province from 2018 to 2023, so as to provide reference for the prevention and control of influenza after COVID-19 pandemic. Throat swab samples of influenza-like illness (ILI) cases from 16 local sentinel hospitals were collected every week, and real-time reverse transcription-polymerase chain reaction (RT-PCR) was used to detect and identify the specific types of influenza viruses. Descriptive epidemiological method was used to analyse the surveillance data from sentinel hospitals and network laboratories. The ILI% were fluctuated between 3.67% and 8.73% from 2018 to 2023 in Zhejiang Province, with a notable increase after COVID-19 pandemic (P < 0.05). The 0–4 years age group had the highest incidence of ILI cases (45.13%), whereas the 5–14 years age group exhibited the highest influenza virus positive rate (26.01%). There were significant differences in temporal distribution and age distribution in ILI% and influenza virus positive rates (P < 0.001). Apart from 2020, the influenza outbreaks in other years displayed a seasonal pattern, with varying predominant strains in different years. During 2020–2022, the correlation between ILI number and the influenza virus positive rate was not statistically significant among 0–4 years age group but it was statistically significant among age groups > 15 years (P < 0.001). The COVID-19 pandemic has markedly influenced the epidemiological characteristics of influenza. Children under 15 years are the focus group for influenza prevention and control. The current definition of ILI may not be appropriate for influenza surveillance in children under 15 years during the COVID-19 pandemic. Continuous influenza surveillance, pay close attention to the changes of influenza virus strains, actively promote the influenza vaccination of key groups and the combination of COVID-19 surveillance in the influenza sentinel surveillance network will play an important role in realizing accurate influenza prevention and control.