Abstract
Summary: A technique for estimating antibodies to the neuraminidase antigens of influenza A is described.The antibody response to the haemagglutinin and neuraminidase antigens of influenza A (H3N2) was studied in a boys' public school over the four-year period 1970–4. During this time there were two outbreaks of influenza A and the effect of antibody on the result of natural challenge was investigated. No boy who had homotypic neuraminidase antibody had clinical influenza.