Abstract
The last influenza pandemic, caused by the swine A(H1N1)pdm09 influenza virus, began in North America at 2009. Since then, the World Health Organization (WHO) recommended integration of the swine-based virus A/California/07/2009 strain in yearly vaccinations. Yet, infections with A(H1N1)pdm09 have continued in subsequent years. The reasons for this are currently unknown. During the 2015–2016 influenza season, we noted an increased prevalence of A(H1N1)pdm09 influenza virus infection in Israel. Our phylogenetic analysis indicated that the circulating A(H1N1)pdm09 strains belonged to 6B.1 and 6B.2 clades and differed from the vaccinating strain, with approximately 18 amino acid differences found between the circulating strains and the immunizing A/California/07/2009 strain. Hemmaglutination inhibition (HI) assays demonstrated higher antibodies titer against the A/California/07/2009 vaccinating strain as compared to the circulating Israeli strains. We thus suggest that the current vaccination was not sufficiently effective and propose inclusion of the current circulating A(H1N1)pdm09 influenza viruses in the annual vaccine composition.
Highlights
Influenza viruses are responsible for many respiratory infections affecting all age groups, the elderly population [1, 2]
Our phylogenetic analysis indicated that the circulating A(H1N1)pdm09 strains belonged to 6B.1 and 6B.2 clades and differed from the vaccinating strain, with approximately 18 amino acid differences found between the circulating strains and the immunizing A/California/07/2009 strain
56.3% were positive for influenza B, 43.01% for A(H1N1)pdm09, and only 0.7% for influenza A(H3N2) (Figure 1)
Summary
Influenza viruses are responsible for many respiratory infections affecting all age groups, the elderly population [1, 2]. Annual epidemics of seasonal influenza viruses are estimated to result in approximately three to five million cases of severe illness and about 250,000 to 500,000 deaths worldwide (WHO, 2014). Influenza virus genome contains 8 single-stranded RNA molecules, which encodes at least 13 proteins, among them Neuraminidase (NA) and Hemagglutinin (HA), which are expressed on the surface of infected cells [3,4,5]. Both the HA and the NA proteins are subjected to extensive antigenic changes, complicating the design of a universal vaccine aiming to target all influenza strains [6]. The primary preventive strategy currently available against influenza virus infection is a vaccine that is designed and administered each year [7]. The vaccine is composed of three or four influenza virus strains prevailing in the influenza season of the opposite hemisphere
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