Antigenic analysis of recent H1N1 influenza viruses with monoclonal antibodies.

: Antigenic analysis of recently isolated H1 influenza viruses was performed using haemagglutination inhibition (HI) assay with monoclonal antibodies to the haemagglutinin (HA) subunit. Tests using monoclonal antibodies against the HA of the A/England/333/80 (H1N1) and A/Yamagata/120/86 (H1N1) viruses revealed that the major antigenic drift occurred in 1985 or 1986 and A/Dunedin/6/83-like virus became a major strain after 1986.