The influenza virus continues to be considered one of the most dangerous respiratory pathogens, and the study of the influenza virus is important for epidemiological control, especially in the case of co-circulation with SARS-CoV-2.
OBJECTIVE
Comparative analysis of influenza viruses isolated from first and severe cases in epidemic seasons before and during the COVID-19 pandemic in Russia.
MATERIAL AND METHODS
The article is based on the results of monitoring the circulation of seasonal influenza viruses obtained in 2019—2023. Samples from the first and severe cases of influenza were studied by PCR diagnostics and full-genome sequencing methods. Antigenic characterization of isolated viruses was performed, and their sensitivity to antiviral drugs was investigated.
RESULTS
The 2019—2020 influenza season in Russia was the last epidemic season before the COVID-19 pandemic with predominant co-circulation of influenza B and influenza A/H1N1pdm09 viruses. After the start of the pandemic, in the 2020—2021 season the influenza virus was virtually absent from circulation in Russia. Virus circulation resumed in the 2021—2022 season with A/H3N2 dominance (clade 3C.2a1b.2a2) and continued in the 2022—2023 season with A/H1N1pdm09 dominance (clade 6B.1A.5a.2a) and the spread of influenza B/Victoria viruses (clade V1A.3a.2), antigenically distinct from the viruses circulating prior to the COVID-19 pandemic. Genetic analysis of D222G/N mutations in the hemagglutinin of A/H1N1pdm09 viruses associated with increased disease severity revealed approximately equivalent selection of D222G and D222N mutations in the 2019—2020 season and increased occurrence of the D222N variant in the 2022—2023 season.
CONCLUSION
The co-circulation with SARS-CoV-2, the return of influenza circulation to epidemic levels, and the emergence of new antigenic variants and pathogenicity factors emphasize the need to monitor and study influenza viruses for epidemiological analysis and prognosis, as well as for the development and application of effective measures to protect the population.