However, the relationship between the changing influenza epidemic and the prevention and control of COVID-19 was unclear.
Influenza, caused by the influenza virus, is an acute respiratory infection that can impose a high burden and cause severe seasonal epidemics or even pandemics.
However, in early 2020, Japan and the United States, among other regions of the Northern Hemisphere, saw a marked decline in influenza activity.
In addition, Australia, Chile and other areas of the Southern Hemisphere shared this observation during the 2020 flu season.
According to our analysis, the COVID-19 epidemic has changed the epidemic trend and characteristics of influenza. During the 2020-2022 COVID-19 pandemic in China, a significant decrease in influenza activity was observed, especially in the winter and spring months.
In addition, seasonality of influenza was evident from 2010 to 2019, but was absent in the 2020/2021 season in China, either in the north or in the south.
Impact of the COVID-19 pandemic on the spread of influenza virus
The reduction of influenza virus infection associated with routine COVID-19 public health interventions in China was concluded after analyzing the epidemiology and seasonal patterns of influenza based on the timeline of available COVID-19 NPIs in China.
Respiratory illnesses often occur during the winter and spring months when COVID-19 and influenza tend to circulate easily. Meanwhile, the resurgence of other respiratory viruses once buried under the COVID-19 NPIs in 2020-2021 has been recognized worldwide.
Thus, the entire population missed the opportunity for enhanced immunity against influenza after the prolonged low flu season during 2020-2022.
As a result, high-risk populations, such as young children and the elderly, become more susceptible to widespread and severe illness from influenza over time.
In addition to increasing influenza vaccination coverage, efforts should be made to strengthen influenza surveillance and establish a comprehensive surveillance system for influenza virus and SARS-CoV-2 to protect these vulnerable populations.
More indicators, such as influenza-positive rate and number of reported cases of influenza, could complete and validate the study. The researchers will also consider using different prediction methods to confirm our results and make relevant additions in the future.