Abstract
Thirty-seven volunteers were inoculated intranasally with living attenuated influenza A2 viruses. Rising titres of circulating antineuraminidase (AN) were detected in 14 of 17 infected volunteers. AN was also found in nasal secretions. Statistical analysis showed that there was a correlation between the titres of haemagglutination-inhibiting antibody (HI) and AN in nasal washings, and between AN in blood and washings. Resistance to infection could be predicted from antibody titres in 29 of 37 volunteers and blood AN alone predicted the outcome of 25 volunteers.