The protective effect of intranasal immunization with inactivated influenza virus vaccine.

Protection against influenza after killed influenza spray vaccine was assessed in nine double blind, placebocontrolled clinical trials and two field studies, involving a total number of 10,000 subjects. Monovalent vaccine, containing 300-360 IU A/Hong Kong/1/68 (H3N2) or bivalent vaccine, containing 300-360 IU A/Aichi/2/68 (H3N2) and 200-240 IU B/Mass/3/66 per dose was used. Administration by the intranasal route appeared to be acceptable as an alternative to the parenteral route. The protective efficacy found was comparable with that attained after parenteral vaccination. It has, however, the advantages of a characteristic lack of side-effects and of the fact that no injection is involved. This will probably enhance the acceptance of influenza immunization by the population and thus lead to a higher vaccination rate in the communities we want to protect against influenza.