Abstract
Influenza virus evolves rapidly due to the accumulated genetic variations on the viral sequence. Unlike in North America and Europe, influenza season in the tropical Southeast Asia spans both the rainy and cool seasons. Thus, influenza epidemiology and viral evolution sometimes differ from other regions, which affect the ever-changing efficacy of the vaccine. To monitor the current circulating influenza viruses in this region, we determined the predominant influenza virus strains circulating in Thailand between January 2016 and June 2017 by screening 7,228 samples from patients with influenza-like illness. During this time, influenza A(H3N2) virus was the predominant influenza virus detected. We then phylogenetically compared the hemagglutinin (HA) gene from a subset of these A(H3N2) strains (n = 62) to the reference sequences and evaluated amino acid changes in the dominant antigenic epitopes on the HA protein structure. The divergence of the circulating A(H3N2) from the A/Hong Kong/4801/2014 vaccine strain formed five genetic groups (designated I to V) within the 3C.2a clade. Our results suggest a marked drift of the current circulating A(H3N2) strains in Thailand, which collectively contributed to the declining predicted vaccine effectiveness (VE) from 74% in 2016 down to 48% in 2017.
Highlights
Influenza A virus is an important respiratory pathogen responsible for the annual influenza outbreak and considerable socio-economic burden on the public healthcare system [1]
Newly emergent A(H3N2) strains identified in this study necessitated further subdivision into a separate group V according to a number of significant variance from the A/Hong Kong/4801/2014 vaccine strain and other previously described variants
Members of group V were characterized by seven amino acid substitutions at N31S, D53N, R142G, S144R, N171K, I192T and Q197H
Summary
Influenza A virus is an important respiratory pathogen responsible for the annual influenza outbreak and considerable socio-economic burden on the public healthcare system [1]. The multivalent influenza virus vaccine administered annually can reduce the risk of morbidity and mortality, but it is dependent on how well the chosen strains included in the vaccine match the strains in circulation [2]. The commonly circulating seasonal influenza A subtypes are A(H1N1)pdm and A(H3N2), of which the latter is reportedly associated with a high rate of hospitalization and mortality in the United States in the 2016–2017 flu season [3]. The hemagglutinin (HA) surface glycoprotein of A(H3N2) possesses defined antigenic and receptor-binding sites [4,5]. The HA diversity resulting from accumulated mutations facilitates.
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