Description
The arrival of SARS-CoV-2 and the preventive measures put in place to reduce its circulation have led to a decrease detections of influenza virus during the 2020-2021 winter season. Changes in the viral aetiology and epidemiological characteristics of respiratory infections during a pandemic need to be explored. This study is a cross-sectional study and the main objective was to determine the rate of influenza virus infection among patients with acute respiratory infection in the 2021-2022 winter season in Corsica (France).
Between December 2021 and March 2022 we collected residual of naso-pharyngeal samples of medical laboratories from symptomatic patients who had been tested for suspected COVID-19 and for whom the results were negative. We analysed these samples for influenza viruses and for a panel of 19 other respiratory pathogens.
We analysed 1707 samples. The median age was 37 years [0-97] with a majority of women 61.6% (N=1051). 400 (23.4%) were positive for at least one of the respiratory viruses tested. Among them, rhinovirus was detected in 37.0% (N=148), influenza A in 19.8% (N=79), coronavirus 229E in 14.2% (N=57), and respiratory syncytial viruses in 13.0% (N=52). The 79 influenza A positive patients had a median age of 22 years [0,89], mainly in the younger age group (0-9 years) (N=21, 26.6%). We had 8.9% (N=7) of influenza A(H1N1)pdm09. After full genome sequencing the strains appear to be close to the A/DARWIN/6/2021 strain of clade 3C.2a1b.2a2 and the Hong Kong/2671/2019 strain of clade 3C.2a1b.1b.
This season was characterized by the resurgence of the circulation of respiratory viruses other than SARS-CoV-2. Influenza A(H3N2) and A(H1N1)pdm09 viruses have co-circulated with a majority of detection in March 2022. The circulation of influenza viruses, appears to have been delayed compared to the years before the appearance of SARS-CoV-2. Prolonged suppression of seasonal respiratory viruses will reduce population immunity and increase severity of future epidemics especially caused by influenza.
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