An Antigenic Analysis Using Monoclonal Antibodies of Influenza A (H3N2) Viruses Isolated from an Epidemic in a Semi-closed Community

Seventy-eight influenza A (H3N2) viruses isolated from a single epidemic in a semi-closed community involving 203 clinical cases were characterized using a panel of monoclonal antibodies to virus haemagglutinin (HA). Thirty groups of antigenically distinguishable viruses were detected but the majority (41%) of the viruses belonged to two serological groupings, designated 11 and 17. Viruses in serological group 11 were present throughout the outbreak. The greatest diversity of antigenic variants occurred at the time of the epidemic peak. Antigenic differences among the HAs of the viruses were also detected using polyclonal human and animal antisera. The electrophoretic mobility of virus-induced structural and non-structural polypeptides and of the RNA of viruses of representative serological groups was very similar or identical, suggesting that new introductions of viruses did not occur during the progress of the epidemic. The evolution of influenza A (H3N2) epidemics even in small communities appears to be complex, although a contribution to the observed antigenic microheterogeneity of the HA by spontaneous variants arising in the laboratory cannot be excluded.