Secretory antibody following oral influenza immunization.

Secretory IgA antibody may be important in protection against respiratory viral infections, and the concept of a common mucosal immune system offers the theoretical basis for the convenient stimulation of this antibody. Therefore, the oral route was compared with intramuscular injection in a double-blind, placebo-controlled study in young healthy volunteers. A killed influenza vaccine, given in enteric-coated capsules (total of 98 ug hemagglutinin of A/Bangkok) led to significant salivary and nasal IgA antibody rises in a 4-week period. The preimmunization titers in secretions were inversely correlated with the antibody rise after immunization. The orally administered vaccine was associated with no more side effects than placebo, in contradistinction to reactions following the intramuscular route. The latter route also was without significant effect in regard to a stimulation of secretory antibodies. The observed simultaneous induction of antibodies in saliva and nasal secretions following oral administration of killed vaccine gives further evidence of a common mucosal immune system and its possible clinical use.