An antigenic variant of the Hong Kong-68 influenza A 2 virus

Both the haemagglutinin and the neuraminidase of influenza A2 virus have undergone progressive antigenic drift since this subtype first appeared in 1957.In 1968 a strain showing a much greater antigenic difference was isolated in Hong Kong. This variant has been responsible for epidemics throughout the world in the past 2 years.In the second year of its prevalence a small proportion of strains isolated showed a small but definite antigenic change, related principally to the haemagglutinin component.This new variant formed about 4% of all strains investigated and was detected in Britain, Portugal, France and New Zealand.