Molecular evolution of influenza A/H3N2 viruses in the province of Quebec (Canada) during the 1997-2000 period

In this study, we compared antigenic (hemagglutination inhibition (HI) assa y) and molecular (sequencing of the hemagglutinin (HAI) gene) characterizat ion of influenza isolates collected in the Province of Quebec (Canada) duri ng the last three flu seasons (1997-2000). Twenty-three isolates were teste d by a standard HI assay and 37 by sequencing of the HAI gene for their hom ology to the A/H3N2 vaccine strains A/Wuhan/359/95 (1997-1998) and A/Sydney /5/97 (1998-1999 and 1999-2000). By HI, two isolates were antigenically sim ilar to A/Wuhan/359/95 (both from 1997 to 1998), 16 were similar to A/Sydne y/5/97 (1997-2000) and no conclusions could be inferred for the other five isolates due to identical HI titers for the two vaccine strains (n = 4) or insufficient viral titer (n = 1). Sequence analysis revealed that four isol ates from 1997 to 1998 were related to A/Wuhan/359/95 whereas the others (n = 4) from 1997 to 1998, as well as all isolates from 1998 to 1999 (n = 18) and 1999 to 2000 (n = 11) were closer to A/Sydney/5/97. The mean number of amino acid differences for the 33 A/Sydney/5/97-like isolates compared wit h the homologous vaccine strain was 6.3 (1.9%), 9.2 (2.8%) and 13.6 (4.1%) for those collected in 1997-1998, 1998-1999, and 1999-2000, respectively. P hylogenetic analysis confirmed that a progressive drift occurred among our A/H3N2 influenza isolates over the last three flu seasons. Furthermore, it revealed that isolates collected during the last two flu seasons were in fa ct more related to A/Panama/2007/99 (2000-2001 vaccine strain) than to A/Sy dney/5/97. Our studies suggest that molecular analysis of the HAI gene shou ld complement the HI assay for a more accurate analysis of influenza A viru s drift. (C) 2001 Elsevier Science B.V. All rights reserved.