Genetic characterization of the hemagglutinin gene of influenza B virus which predominated in the 1985/86 Canadian influenza season.

OBJECTIVE

To characterize the hemagglutinin (HA) gene of B/Canada/3/85, a prototype strain of influenza B virus variants that emerged in the 1984/85 influenza season and predominated in the 1985/86 season in Canada.

DESIGN

Sequencing and comparison of the HA genes of B/Canada/3/85 and the vaccine strains for the 1985/86 season, B/USSR/100/83, and for the 1986/87 season, B/Ann Arbor/1/86.

RESULTS

B/Canada/3/85 was similar to B/Ann Arbor/1/86 and significantly different from B/USSR/100/83. Phylogenetic analysis of the HA1-coding sequences indicated that B/Canada/3/85 and several other 1985 strains isolated in distant parts of the world were very closely related and were early variants representing the emergence of a new lineage, the B/Victoria/2/87 lineage. B/Canada/3/85 differed from B/USSR/100/83 in nucleotide sequence by 3.44% and in amino acid sequence by 3.33%. There was also an insertion of two amino acids in the HA1 region of B/Canada/3/85.

CONCLUSIONS

B/Canada/3/85 was one of the herald strains for the 1985/1986 influenza B epidemic. The amino acid mutations and the two-codon insertion together may account for the observed antigenic changes in the HA of the influenza B variants.