Decreased seasonal influenza during the COVID-19 pandemic in temperate countries

Epidemiological characteristics of seasonal influenza under implementation of zero-COVID-19 strategy in China

OBJECTIVE

Respiratory viral diseases have posed a persistent threat to public health due to their high transmissibility. Influenza virus and SARS-Cov-2 are both respiratory viruses that have caused global pandemics. A zero-COVID-19 strategy is a public health policy imposed to stop community transmission of COVID-19 as soon as it is detected. In this study, we aim to examine the epidemiological characteristics of seasonal influenza in the past five years before and after the emergence of COVID-19 in China and observe the possible impact of the strategy on influenza.

METHODS

Data from two data sources were retrospectively analyzed. A comparison on influenza incidence rate between Hubei and Zhejiang provinces was conducted based on data from the Chinese Center for Disease Control and Prevention (CDC). Then a descriptive and comparative analysis on seasonal influenza based on data from Zhongnan Hospital of Wuhan University and Hangzhou Ninth People`s Hospital before and after the outbreak of SARS-CoV-2 was conducted.

RESULTS

From 2010-2017, both provinces experienced relatively low influenza activity until the 1st week of 2018, when they reached peak incidence rates of 78.16/100000PY, 34.05/100000PY respectively. Since then, influenza showed an obvious seasonality in Hubei and Zhejiang until the onset of COVID-19. During 2020 and 2021, there was a dramatic decline in influenza activity compared to 2018 and 2019. However, influenza activity seemed to rebound at the beginning of 2022 and surged in summer, with positive rates of 20.52% and 31.53% in Zhongnan Hospital of Wuhan University and Hangzhou Ninth People`s Hospital respectively as of the time writing this article.

CONCLUSIONS

Our results reinforce the hypothesis that zero-COVID-19 strategy may impact the epidemiological pattern of influenza. Under the complex pandemic situation, implementation of NPIs could be a beneficial strategy containing not only COVID-19 but also influenza.

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