Abstract
ABSTRACT The spread of influenza A/H3N2 variants possessing the hemagglutinin 121 K mutation and the unexpectedly high incidence of influenza in the 2017–2018 northern hemisphere influenza season have raised serious concerns about the next pandemic. We summarized the national surveillance data of seasonal influenza in China and identified marked differences in influenza epidemics between northern and southern China, particularly the predominating subtype and the presence of an additional summer peak in southern China. Notably, a minor spring peak of influenza caused by a different virus subtype was also observed. We also revealed that the 3C.2a lineage was dominant from the summer of 2015 to the end of the 2015–2016 peak season in China, after which the 3C.2a2 lineage predominated despite the importation and co-circulation of the 121 K variants of 3C.2a1 and 3C.2a3 lineages at the global level. Finally, an analysis based on genetic distances revealed a delay in A/H3N2 vaccine strain update. Overall, our results highlight the complicated circulation pattern of seasonal influenza in China and the necessity for a timely vaccine strain update worldwide.
Highlights
IntroductionInfluenza activity differs between southern and northern China, with two peaks (winter and summer) in southern China and only a single peak (winter) in northern China [1]
Influenza activity differs between southern and northern China, with two peaks in southern China and only a single peak in northern China [1]
To provide a more comprehensive study of the genetic diversity and antigenic variation of A/H3N2, and to trace the origin and spread of the novel 121 K variant in China, we present a description of the national surveillance data of influenza-like illnesscombined with the sequence data of 1471 full-length genomes of A/ H3N2 influenza A virus isolated across China since 2015
Summary
Influenza activity differs between southern and northern China, with two peaks (winter and summer) in southern China and only a single peak (winter) in northern China [1]. A novel genetic variant with a N121 K mutation in the hemagglutinin (HA) protein emerged in Hong Kong and comprised more than 35% of the A/H3N2 viruses tested in May 2017 [2]. This mutation was located in epitope D, and variants possessing this mutation were reported to have a less vaccine effectiveness in Denmark in the 2016–2017 influenza season [9]. A recent study suggested that most of the global population would be susceptible to the 121 K variants [10]. This variant has been widely spread across Europe [7,9,11], Asia [2,8,12] and North America [13]
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