Evolution of surface and nonstructural-1 genes of influenza B viruses isolated in the Province of Québec, Canada, during the 1998-2001 period.

After 2 minor winter seasons, influenza B viruses were predominantly isolated in the Province of Quebec, Canada, during the 2000-2001 season representing 74% of laboratory-confirmed influenza viruses. We performed an antigenic study of the hemagglutinin (HA) protein and a molecular characterization of the HA1 region, nonstructural-1 (NS1) and neuraminidase (NA)/NB genes of 20 influenza B strains isolated in the Province of Quebec during the 1998-2001 period. Our isolates were compared to recent vaccine strains (B/Harbin/7/94 in 1998-1999, B/Yamanashi/166/98 in 1999-2000 and 2000-2001, and B/Sichuan/379/99 in 2001-2002). The hemagglutination inhibition (HI) test revealed that all isolates were different from B/Harbin/7/94 and were more related to the 2 other vaccine strains although precise identification was often impossible. Molecular analysis of the HA1 gene revealed that both B/Yamanashi/166/98-like and B/Sichuan/379/99-like isolates co-circulated during the 1998-1999 season whereas isolates from the 2 subsequent years were more related to B/Sichuan/379/99. Most isolates (8/9) of the 2000-2001 season contained a N126D substitution recently associated with altered antigenicity in recent influenza B/Yamagata/16/88-related viruses. Although the HA1 and NS1 protein sequences of viruses isolated during the 1998-1999 season were clearly different from those of the respective vaccine strain (B/Harbin/7/94), the NA protein sequence of those isolates was slightly more related to B/Harbin/7/94 than B/Yamanashi/166/98 suggesting distinct patterns of evolution for these genes. This study confirms the importance of a detailed molecular analysis for understanding the evolution of influenza B viruses.