[Long-term effect of oral immunization against influenza with a gamma ray-inactivated vaccine in mice].

NMRI-mice were immunized orally twice within 10 days with an influenza vaccine (A/PR/8/34), inactivated by gamma radiation (total doses = 1.5 kGy). The immunization with a relatively low doses (about 20 micrograms hemagglutinin/mouse) led to the occurrence of low specific antibody titer in the lung lavage fluid till 6th month. Despite of the low titer, immunized mice were protected against aerogenic infection for about 6 months. Protection was demonstrated in comparison to non-immunized mice by a limited increase of cells in broncho-alveolar lavage, low virus titer in the lung and survival of most animals after a lethal aerosol challenge with the live virus.