IntroductionLiterature on influenza focuses on influenza A, despite influenza B having a large public health impact. The Global Influenza B Study aims to collect information on global epidemiology and burden of disease of influenza B since 2000.MethodsTwenty-six countries in the Southern (n = 5) and Northern (n = 7) hemispheres and intertropical belt (n = 14) provided virological and epidemiological data. We calculated the proportion of influenza cases due to type B and Victoria and Yamagata lineages in each country and season; tested the correlation between proportion of influenza B and maximum weekly influenza-like illness (ILI) rate during the same season; determined the frequency of vaccine mismatches; and described the age distribution of cases by virus type.ResultsThe database included 935 673 influenza cases (2000–2013). Overall median proportion of influenza B was 22·6%, with no statistically significant differences across seasons. During seasons where influenza B was dominant or co-circulated (>20% of total detections), Victoria and Yamagata lineages predominated during 64% and 36% of seasons, respectively, and a vaccine mismatch was observed in ≈25% of seasons. Proportion of influenza B was inversely correlated with maximum ILI rate in the same season in the Northern and (with borderline significance) Southern hemispheres. Patients infected with influenza B were usually younger (5–17 years) than patients infected with influenza A.ConclusionInfluenza B is a common disease with some epidemiological differences from influenza A. This should be considered when optimizing control/prevention strategies in different regions and reducing the global burden of disease due to influenza.

The hemagglutinin (HA) is a major influenza virus antigen, which, once recognized by antibodies and substitutions in HA genes, helps virus in escaping the human immune response. It is therefore critical to perform genetic and phylogenetic analysis of HA in circulating influenza viruses. We performed phylogenetic and genetic analysis of isolates from Ukraine, the vaccine strain and reference strains were used to phylogenetically identify trends in mutation locations and substitutions. Ukrainian isolates were collected between 2009–2017 and clustered in the influenza genetic groups 2, 6, 7, and 8. Genetic changes were observed in each of the antigenic sites: Sa – S162T, K163Q, K163I; Sb – S185T, A186T, S190G, S190R; Ca1 – S203T, R205K, E235V, E235D, S236P; Ca2 – P137H, H138R, A141T, D222G, D222N; Cb – A73S, S74R, S74N. In spite of detected mutations in antigenic sites, Ukrainian isolates retained similarity to the vaccine strain A/California/07/09 circulated during 2009–2017. However, WHO recommended a new vaccine strain A/Michigan/45/2015 for the Southern Hemisphere after the emergence of the new genetic groups 6B.1 and 6B.2. Our study demonstrated genetic variability of HA protein of A(H1N1)pdm09 viruses isolated in 2009–2017 in Ukraine. Influenza surveillance is very important for understanding epidemiological situations.

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The article presents results of genetic analysis of influenza viruses genes – hemagglutinin and neuraminidase, isolated in Ukraine in 2012-2015 years. Influenza viruses had mutations observed during all investigated epidemic seasons and acquired new substitutions, which were saved in next years or not consolidated.

Human type A influenza viruses A(H1N1)pdm09 have caused seasonal epidemics of influenza since the 2009–2010 pandemic. A(H1N1)pdm09 viruses had a leading role in the severe epidemic season of 2015/16 in the Northern Hemisphere and caused a high incidence of acute respiratory infection (ARI) in Ukraine. Serious complications of influenza-associated severe ARI (SARI) were observed in the very young and individuals at increased risk, and 391 fatal cases occurred in the 2015/16 epidemic season. We analyzed the genetic changes in the genomes of A(H1N1)pdm09 influenza viruses isolated from SARI cases in Ukraine during the 2015/16 season. The viral hemagglutinin (HA) fell in H1 group 6B.1 for all but four isolates, with known mutations affecting glycosylation, the Sa antigenic site (S162N in all 6B.1 isolates), or virulence (D222G/N in two isolates). Other mutations occurred in antigenic site Ca (A141P and S236P), and a subgroup of four strains were in group 6B.2, with potential alterations to antigenicity in A(H1N1)pdm09 viruses circulating in 2015/16 in Ukraine. A cluster of Ukrainian isolates exhibited novel D2E and N48S mutations in the RNA binding domain, and E125D in the effector domain, of immune evasion nonstructural protein 1 (NS1). The diverse spectrum of amino-acid substitutions in HA, NS1, and other viral proteins including nucleoprotein (NP) and the polymerase complex suggested the concurrent circulation of multiple lineages of A(H1N1)pdm09 influenza viruses in the human population in Ukraine, a country with low vaccination coverage, complicating public health measures against influenza.