Abstract
BackgroundThe direct effect of antigenic site mutations in influenza viruses on antigenic drift and vaccine effectiveness is poorly understood.ObjectiveTo investigate the genetic and antigenic characteristics of human influenza A (H3N2) viruses circulating in Ontario during the early 2010–2011 winter season.Study designWe sequenced the hemagglutinin (HA) and neuraminidase (NA) genes from 41 A(H3N2) viruses detected in nasopharyngeal specimens. Strain typing was performed by hemagglutination inhibition (HI) assay. Molecular and phylogenetic tree analyses were conducted.ResultsHA and NA genes showed high similarity to the 2010–2011 vaccine strain, A/Perth/16/2009 (H3N2)-like virus (97·7–98·5% and 98·7–99·5% amino acid (AA) identity, respectively). Compared to A/Perth/16/2009 strain, HA gene mutations were documented at 28 different AA positions across all five H3 antigenic sites, with a range of 5–11 mutations in individual viruses. Thirty-six (88%) viruses had 8 AA substitutions in common; none of these had reduced HI titer. Among Ontario isolates, 11 antigenic site AAs were positively selected with an increase in glycosylation sites.ConclusionThe presence of antigenic site mutations with high frequency among 2010–2011 influenza H3N2 isolates confirms ongoing adaptive H3N2 evolution. These may represent early phylogenetic changes that could cause antigenic drift with further mutations. Clinical relevance of antigenic site mutations not causing drift in HI assays is unknown and requires further investigation. In addition, viral sequencing information will assist with vaccine strain planning and may facilitate early detection of vaccine escape.
Highlights
All age groups are infected by influenza viruses, most of the influenza-related hospitalizations occur in young children (65 years of age), and most deaths are reported in the elderly.[3]
The current study reports the HA genetic and antigenic relatedness between H3N2 viruses circulating during August 2010 to January 2011 in Ontario and A/Perth/16/2009(H3N2)-like virus (A/Perth/16/2009), which was recommended as the H3N2 component of the 2010–2011
We extended this study to understand the mutational trends at antigenic sites of global influenza A viruses (IAV) (H3N2) isolates from 2010–2011, which were grouped by continent
Summary
Influenza viruses are considered one of the most common causes of respiratory infection among humans.[1,2] all age groups are infected by influenza viruses, most of the influenza-related hospitalizations occur in young children (65 years of age), and most deaths are reported in the elderly.[3]. The direct effect of antigenic site mutations in influenza viruses on antigenic drift and vaccine effectiveness is poorly understood
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