The production of neutralizing activity in serum and nasal secretion following immunization with influenza B virus.

Trials were made in volunteers in 1967 and 1968 of various virus vaccines against influenza virus B. Sera and serially collected nasal washings before and after immunization were tested respectively for haemagglutination-inhibiting and tissue culture virus-neutralizing antibodies to the same strain of influenza B/Eng/65 virus as that used in the vaccines. Infection, as determined by recovery of virus and serological changes following intranasal instillation of attenuated live virus, was accompanied by the subsequent appearance of neutralizing antibodies in nasal secretion. Inactivated vaccine subcutaneously did not evoke nasal antibody formation in 1967 but did so in 1968.In 1968 intranasal challenge of the volunteers with the attenuated virus 1 month after immunization demonstrated a correlation of susceptibility or resistance to infection with nasal and serum antibodies. Resistance appeared to depend either on a high level of serum antibodies or nasal antibodies, or both.