@Article{info:doi/10.2196/47370,
author="Jiang, Mingyue
and Jia, Mengmeng
and Wang, Qing
and Sun, Yanxia
and Xu, Yunshao
and Dai, Peixi
and Yang, Weizhong
and Feng, Luzhao",
title="Changes in the Epidemiological Features of Influenza After the COVID-19 Pandemic in China, the United States, and Australia: Updated Surveillance Data for Influenza Activity",
journal="Interact J Med Res",
year="2024",
month="Oct",
day="9",
volume="13",
pages="e47370",
keywords="influenza; seasonal variation; COVID-19 pandemic; stringency index",
abstract="Background: There has been a global decrease in seasonal influenza activity since the onset of the COVID-19 pandemic. Objective: We aimed to describe influenza activity during the 2021/2022 season and compare it to the trends from 2012 to 2023. We also explored the influence of social and public health prevention measures during the COVID-19 pandemic on influenza activity. Methods: We obtained influenza data from January 1, 2012, to February 5, 2023, from publicly available platforms for China, the United States, and Australia. Mitigation measures were evaluated per the stringency index, a composite index with 9 measures. A general additive model was used to assess the stringency index and the influenza positivity rate correlation, and the deviance explained was calculated. Results: We used over 200,000 influenza surveillance data. Influenza activity remained low in the United States and Australia during the 2021/2022 season. However, it increased in the United States with a positive rate of 26.2{\%} in the 49th week of 2022. During the 2021/2022 season, influenza activity significantly increased compared with the previous year in southern and northern China, with peak positivity rates of 28.1{\%} and 35.1{\%} in the second week of 2022, respectively. After the COVID-19 pandemic, the dominant influenza virus genotype in China was type B/Victoria, during the 2021/2022 season, and accounted for >98{\%} (24,541/24,908 in the South and 20,543/20,634 in the North) of all cases. Influenza virus type B/Yamagata was not detected in all these areas after the COVID-19 pandemic. Several measures individually significantly influence local influenza activity, except for influenza type B in Australia. When combined with all the measures, the deviance explained values for influenza A and B were 87.4{\%} (P<.05 for measures of close public transport and restrictions on international travel) and 77.6{\%} in southern China and 83.4{\%} (P<.05 for measures of school closing and close public transport) and 81.4{\%} in northern China, respectively. In the United States, the association was relatively stronger, with deviance-explained values of 98.6{\%} for influenza A and 99.1{\%} (P<.05 for measures of restrictions on international travel and public information campaign) for influenza B. There were no discernible effects on influenza B activity in Australia between 2020 and 2022 due to the incredibly low positive rate of influenza B. Additionally, the deviance explained values were 95.8{\%} (P<.05 for measures of restrictions on gathering size and restrictions on international travel) for influenza A and 72.7{\%} for influenza B. Conclusions: Influenza activity has increased gradually since 2021. Mitigation measures for COVID-19 showed correlations with influenza activity, mainly driven by the early stage of the pandemic. During late 2021 and 2022, the influence of mitigation management for COVID-19 seemingly decreased gradually, as the activity of influenza increased compared to the 2020/2021 season. ",
issn="1929-073X",
doi="10.2196/47370",
url="https://www.i-jmr.org/2024/1/e47370",
url="https://doi.org/10.2196/47370",
url="http://www.ncbi.nlm.nih.gov/pubmed/39382955"
}