HA1-DOMAIN OF INFLUENZA-A (H3N2) VIRUSES IN FINLAND IN 1989-1995 - EVOLUTION, EGG-ADAPTATION AND RELATIONSHIP TO VACCINE STRAINS

The HA1 gene sequences of 22 MDCK cell-derived influenza A (H3N2) stra ins, ten of their egg-derived counterparts and three vaccine strains w ere determined. Antigenic and sequence differences between the epidemi c and vaccine strains were recorded, most striking in 1992/93; a minor ity of the amino acid differences in 1989-95 was involved in egg-adapt ation. Changes in the assortment of amino acid substitutions produced during egg-adaptation of field strains may account for the difficulty encountered in isolating these viruses in embryonated eggs. Six revert ant amino acids, characteristic of field strains prevalent in 1969-71 were recorded in 1994/95. Their genome sequence was interpreted to hav e been maintained over the interval years among low abundant sequences of the viral quasispecies. Potential changes of carbohydrate moieties were recorded in two glycosylation sites, suggesting that oligosaccha rides at these sites are not necessarily advantageous for the H3N2 sub type virus currently.