SEVERE CASES OF SEASONAL INFLUENZA IN RUSSIA IN 2015 - 2016 AND 2016 - 2017

Abstract

Aim. Evaluation of seroprevalence of antibodies to influenza A and В viruses and analysis of specimens from severe or fatal influenza cases in Russia in 2015 - 2016 and 2016 - 2017 flu seasons. Materials and methods. Determination of antibody titer in human serum samples in hemagglutination inhibition assay with reference antigens. Isolation of influenza viruses from nasopharyngeal swabs and autopsy material in cell culture. Characterization ofisolated strains. Results. In 2016, compared to 2015, the proportion of serum samples, containing antibodies to influenza viruses A(H 1N1 pdm09) and A(H3N2), increased. During the 2015-2016 season, elevated number of severe and fatal cases of influenza were registered. The majority of circulated strains belonged to the new clade 6B.1 of A(HlNippdm09 viruses. 1% of analyzed isolates carried H275Y amino acid substitution in neuraminidase and were resistant to oseltamivir. In the 2016 - 2017 season, there were less severe cases of influenza. The most prevalent were influenza viruses A(H3N2) and B/Victoria. Isolated H3N2 viruses belonged to the 3C.2a subclade and B/Victoria isolates were from the 1A genetic group. All tested strains were susceptible to neuraminidase inhibitors. Conclusions. Flu seasons 2015 - 2016 and 2016 - 2017 differed in intensity of influenza activity and in the dominant influenza A virus subtype. Immunization with vaccine, comprising new HlNlpdm09-component, is crucial for prophylaxis of influenza infection with viruses from 6B. 1 subclade in the next season. Neuraminidase inhibitors are recommended for influenza treatment.