Effect of neuraminidase antibody on Hong Kong influenza.

The relation between antineuraminidase antibody (A.N.) and natural influenza infection in 1968 was investigated in the community of Tecumseh, Michigan. The outbreak was caused by Hong Kong influenza virus, which contained a new hæmagglutinin antigen (H3), while the neuraminidase antigen (N2) was more closely related to that of Asian viruses circulating since 1957. In the study group of two hundred and seventy-four randomly selected adults (aged 20-45), titres of N2 neuraminidase antibody were detected in a hundred and fifteen (42%) serum samples collected before the outbreak. Influenza infection during the course of the outbreak was identified serologically. The frequency of infection decreased significantly at increasing levels of pre-existing A.N. antibody. In those subjects who