[The viruses of the 1952-3 influenza epidemic].

The results of antigenic studies of the viruses received at the World Influenza Centre from the 1952-3 influenza epidemic are described. As in 1950-1, two main antigenic groups of influenza A viruses could be distinguished. One group, called Liverpool, contained strains closely related to 1950-1 Liverpool strains. The other, called Scandinavian, contained strains related to but not identical with 1950-1 Scandinavian viruses. Altogether, 175 Scandinavian, 33 Liverpool, and 4 influenza B virus strains were examined.A peculiar relationship between 1950-1 and 1952-3 Scandinavian viruses was investigated by antibody absorption experiments. It was concluded that A/Sweden/3/50 and A/Missouri/303/52 viruses had a rather similar antigenic composition, but that the dominant antigen in the former strain was contained within the virus particle whereas it was a surface constituent of the latter strain. The possible significance of this finding in the antigenic evolution of influenza viruses is discussed.The findings suggest that survival of influenza viruses without much antigenic alteration from one epidemic to the next, two years later, is a demonstrable but uncommon finding. Evidence is presented that this survival was followed by separate spread of each antigenic variety of virus in different countries.