The antibody responses to influenza virus A/PR/8/34 HA
vaccine and protection against virus challenge in mice given the
vaccine together with the B subunit of
cholera toxin (CTB) intranasally were compared with those in mice given the
vaccine with CTB perorally, intraperitoneally or subcutaneously. Intranasal vaccination induced remarkably higher levels of
antiviral IgA antibodies in both respiratory washings and serum than did other routes of vaccination. The titres of
antiviral IgG antibodies in respiratory washings and serum, and haemagglutination-inhibiting (HI)
antibodies in serum, were similar after intranasal and parenteral vaccination. Oral vaccination, however, induced low levels of
antiviral IgG antibodies but no detectable HI
antibodies. Moreover, intranasal immunization elicited significantly higher titres of
antiviral IgA antibodies in intestinal secretions in comparison with oral immunization. In contrast, parenteral immunization failed to induce these
IgA antibodies. In virus challenge studies, a greater protective effect was seen after intranasal and intraperitoneal vaccination than after other routes of vaccination. These results suggest that intranasal inoculation of combined HA
vaccine and CTB is superior to oral or parenteral inoculation in protecting mice. Furthermore, the intestinal
antiviral IgA responses suggest that
intranasal administration of CTB-
combined vaccines could be effective not only against respiratory pathogens but also against enteropathogens.