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