Identification of H3N2 NA and PB1-F2 genetic variants and their association with disease symptoms in the 2014-15 influenza season

The 2014-15 influenza season saw the emergence of an antigenic drift variant of H3N2 which formed the 3C.2a HA clade. Nasopharyngeal swabs from patients with confirmed influenza A virus infection were used for whole viral genome sequencing to make HA clade calls and identify mutations in the NA (a new glycosylation site, NAg+) and PB1-F2 (H75P mutation). The mutations in NA and PB1-F2 that were present in a subset of clade 3C.2a viruses (NAg+F2P) which came to dominate in the subsequent influenza season. The NAg+F2P genotype viruses were associated with increased wheezing and shortness of breath in infected patients. The use of primary human nasal epithelial cell cultures allowed for more efficient isolation of H3N2 viruses and identified replication differences between H3N2 genotypes. The use of sequencing of clinical samples combined with in vitro analysis of virus replication provided a unique system for identifying and characterizing novel variants of influenza A virus