The value of influenza vaccine remains controversial in spite of its long availability and use. By the standards used for judging many other vaccines, its performance has not been good. Immunity is short-lived, and frequent revaccination is required. Also, it is not universally accepted that the vaccine has value for civilian populations even though its effectiveness in military groups appears to be established.
Complicating the problem of evaluating influenza vaccine is the renewed interest in antibody produced locally in the respiratory tract. Recent work suggests that local antibody may be of critical importance in immunity to several respiratory infections, including influenza,1 and that vaccines must stimulate antibody in the respiratory tract to be effective.
It was with this background that Hong Kong influenza appeared in 1968. The emergence of this new strain provided an opportunity for studying influenza vaccine under field conditions during an epidemic. One such study, which