Genetic divergence of influenza A(H3N2) amino acid substitutions mark the beginning of the 2016-2017 winter season in Israel

BACKGROUND: Influenza vaccine composition is reevaluated each year due to the frequency and accumulation of genetic changes that influenza viruses undergo. The beginning of the 2016-2017 influenza surveillance period in Israel has been marked by the dominance of influenza A(H3N2). OBJECTIVES: To evaluate the type, subtype, genetic evolution and amino acid substitutions of influenza A(H3N2) viruses detected among community patients with influenza-like illness (ILI) and hospitalized patients with respiratory illness in the first weeks of the 2016-2017 influenza season. STUDY DESIGN: Respiratory samples from community patients with influenza-like illness and from hospitalized patients underwent identification, subtyping and molecular characterization. Hemagglutinin sequences were compared to the vaccine strain, phylogenetic tree was created, and amino acid substitutions were determined. RESULTS: Influenza A(H3N2) predominated during the early stages of the 2016-2017 influenza season. Noticeably, approximately 20% of community patients and 36% of hospitalized patients, positive for influenza3), received the 2016-2017 influenza vaccine. The influenza A(H3N2) viruses demonstrated genetic divergence from the vaccine strain into three separate subgroups within the 3C.2a clade. One resembled the new 3C.2a1 subclade, one resembled the recently proposed 3C.2a2 subclade and the other was not previously described. Diversity was observed within each subgroup, in terms of additional amino acid substitutions. CONCLUSIONS: Characterization of the 2016-2017 A(H3N2) influenza viruses is imperative for determining the future influenza vaccine composition.