EFFECTIVE IMMUNIZATION WITH LIVE ATTENUATED INFLUENZA-A VIRUS CAN BE ACHIEVED IN EARLY INFANCY

The immunogenicity of vaccines can be modified in infancy by maternal antibodies and other immunizations, Hence, the safety and immunogenici ty of two doses of 10(7) TCID50 of live, attenuated cold-adapted (ca) influenza A/Kawasaki/86 (H1N1) reassortant virus vaccine given with or apart from childhood immunizations were evaluated in infants, startin g at 2, 4, or >6 months of age, in randomized, double-blind trials, Th e ca vaccine was safe and did not significantly reduce the immunogenic ity of the childhood vaccines in these infants. Infectivity of ca viru s (virus shedding, greater than or equal to 4-fold rise in serum hemag glutination inhibition antibody titer, or both) was affected by age, q uantity of ca virus given, and prior ca virus infection. Two doses of 10(7) TCID50 of ca influenza virus infected all infants, indicating th at both doses are probably needed to achieve immunity against influenz a in infants <6 months of age.