Multidose, live attenuated, cold-recombinant, trivalent influenza vaccine in infants and young children.

Twenty-two healthy infants and children received either cold-recombinant, trivalent influenza vaccine or placebo in a three-dose vaccine trial. Most (82%) who received vaccine were seronegative to all three vaccine strains (10(6) TCID50/dose each): A/Kawasaki/9/86 (H1N1), A/Los Angeles/2/87 (H3N2), and B/Yamagata/16/88. Vaccine was administered intranasally at time 0 and 2 and 4 months later. The vaccine was well tolerated and immunogenic when administered in a multidose regimen. The first dose stimulated antibody to H1, H3, and B in 59%, 94%, and 35% of vaccinees, respectively, by hemagglutination inhibition (HAI) or ELISA. After two doses of vaccine, 93%, 93%, and 80% had antibody by HAI or ELISA to H1, H3, and B, respectively. Most vaccinees (67%) responded to all three viruses after two doses of vaccine. The third dose contributed little to the vaccine's immunogenicity. Multidose trivalent influenza vaccine is safe and induces an immune response in most vaccinees after two doses.