CONCURRENT ANTIGENIC ANALYSIS OF RECENT EPIDEMIC INFLUENZA-A AND INFLUENZA-B VIRUSES AND QUANTITATION OF ANTIBODIES IN POPULATION SEROSURVEYS IN ITALY

Laboratory investigations of virus isolation and serum antibodies in a Mediterranean country (Italy) demonstrated that influenza A and B vir uses, and often both, circulated every winter in Italy. The winter 198 7/88 was characterized by a low level of influenza activity, as shown by the limited number (47) of influenza virus isolates, the majority o f which (61%) belonged to the influenza B type. In contrast, the 1988/ 89 influenza season was exclusively associated with the circulation of influenza type A viruses. The A(H1H1) subtype was largely predominant (97%), as compared to the low incidence of the A(H3N2) subtype (3%). During the 1989/90 winter a co-circulation of A and B influenza viruse s was observed, A(H3N2) strains being responsible for 96% of the virol ogically confirmed cases. Antigenic analysis of the virus isolates sho wed some antigenic variation in influenza A viruses of both H1N1 and H 3N2 subtypes, whilst antigenic stability was found among the influenza B virus isolates. Overall, the above virological findings correlate w ith the data concerning the pattern of influenza virus circulation in Northern Europe and the UK during the three years surveyed. The result s of serum antibody surveys conducted in each post-epidemic period are also reported.