Antigenic and molecular surveillance of influenza virus strains in the period 1992-1993

Abstract

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In the framework of the influenza virus surveillance of RIVM we have examined 195 influenza virus strains isolated in various European countries and Japan during the season 1992/93. Haemagglutination inhibition (HI) assasys showed the H3N2-virus strains to come into two groups of roughly equal sizes. One group was similar to the strains circulating in 1991/92, including the vaccine strain of the season 1992/93, whereas the other group belonged to a new variant, typified by strain A/Beijing/32/92. The antigenic difference between the two groups was unusually large for two contemporary variants of H3N2-virus. This implicates that people, even when infected with influenza virus A (H3N2) in 1991/92 or vaccinated in November 1993, were poorly protected against the new virus variant. Probably this explains the high number of excess deaths (1800) that was observed in the Netherlands early in 1993. Interestingly, antigenic as well as molecular analysis demonstrated a relationship between the new virus variant and sporadically circulating deviant H3N2-viruses from Chine, Singapore, and France isolated in 1990 and early 1991. During the epidemic, in the Netherlands two other H3N2-virus strains were isolated which apparently originated from pigs. The numerous influenza B virus strains and the few Influenza A (H1N1) virus strains isolated in 1992/93 well matched the respective vaccine strains used in this season.