Antigenic variability of influenza viruses A and B isolated from children in Saint-Petersburg in the period 2013–2015

Purpose of the study: study of the circulation, isolation and antigenic analysis of influenza viruses A and B in St.-Petersburg in the children aged 0–18 in the seasons 2013–2015.Materials: nasal swabs from children-inpatients from Saint-Petersburg.Methods: virus isolation in MDCK cell culture and chicken embryos, antigenic analysis with the hemagglutination inhibition (HAI) test with the set of hyper-immune rat antisera to the epidemic and reference strains, antigenic cartography.Results: The epidemic seasons 2013–2015 were characterized by the co-circulation in children in St.-Petersburg of influenza sub-types А(H1N1)pdm09, A(H3N2), and B of Yamagata lineage (B yam). In the season 2014–2015 the low activity of epidemic process was observed with the predominant sub-type A(H3N2) and in the next season – 2014–2015 with the more pronounced epidemic activity – the pre-dominance of B yam viruses. Antigenic analysis of influenza viruses А(H1N1)pdm09 which circulated in children revealed their antigenic homogeneity and full correspondence with vaccine strain A/California/07/09. As for А(H3N2) viruses, two antigenic groups were established: strains similar to A/St.-Petersburg/80/14 (sub-clade 3C.2a) and strains similar to A/Switzerland/9715293/13 (sub-clade 3C.3a). А(Н3N2) strains of the season 2013-2014 were similar to the vaccine strain. However isolates of the season 2014-2015 did not fit to the vaccine strain because in the children were predominant strains similar to the evolution branch A/St.-Petersburg/80/14 while according the WHO recommendations the influenza vaccine contained the strain A/Texas/50/12. Antigenic analysis of influenza viruses B showed their homogeneity and all they were B/Phuket/3073/13-like. Influenza strains B also incompletely corresponded to the vaccine strain – B/Massachusetts/2/12 belonging to the different genetic sub-clade. That might be the reason of enhanced morbidity of children with influenza B in the last season.Conclusion: The obtained results stress the urgency for the wide coverage of human population with the epidemic studies, virus isolation in different time periods and geographic regions and their etiological studies with the modern techniques. Only in these conditions we can assure high efficiency of flu seasonal vaccines.