Recombinant cold-adapted attenuated influenza A vaccines for use in children: reactogenicity and antigenic activity of cold-adapted recombinants and analysis of isolates from the vaccinees.

Reactogenicity and antigenic activity of recombinants obtained by crossing cold-adapted donor of attenuation A/Leningrad/134/47/57 with wild-type influenza virus strains A/Leningrad/322/79(H1N1) and A/Bangkok/1/79(H3N2) were studied. The recombinants were areactogenic when administered as an intranasal spray to children aged 3 to 15, including those who lacked or had only low titers of pre-existing anti-hemagglutinin and anti-neuraminidase antibody in their blood. After two administrations of vaccines at a 3-week interval, both strains induced antibody in 75 to 95% of the children. On coinfection of chicken embryos with both recombinants, only weak interference was observed. Administration to children of the bivalent vaccine containing H1N1 and H3N2 recombinants induced efficient production of antibody to H1 and H3 hemagglutinins and N1 and N2 neuraminidases without adverse reactions. The recombinants studied were genetically stable as judged by retention of the temperature-sensitive phenotypes and a lack of reversion of the genes carrying temperature-sensitive mutations in all of the reisolates from vaccinated children.