STUDIES ON REACTOGENICITY AND IMMUNOGENICITY OF ATTENUATED BIVALENT COLD RECOMBINANT INFLUENZA TYPE-A (CRA) AND INACTIVATED TRIVALENT INFLUENZA-VIRUS (TI) VACCINES IN INFANTS AND YOUNG-CHILDREN

Fifty-two infants seronegative to or without prior infection with influenza type A viruses were enrolled in a study to evaluate reactogenicity and immunogenicity of three bivalent cold recombinant type A (CRA) and two trivalent inactivated influenza (TI) vaccines. Controls consisted of infants receiving normal saline by nose drops (Pl(i.n.)) or intramuscularly (Pl(i.m.)). CRA and TI vaccinees were monitored for local and systemic reactions after vaccination. Serum specimens obtained prior to and 6 weeks postvaccination were analysed for neutralizing antibody to influenza H1N1 and H3N2 viruses. CRA vaccinees and Pl(i.n.) recipients had similar numbers of acute respiratory infections and comparable rates of illnesses during the trial. Significantly fewer CRA vaccinees without an intercurrent viral infection had fever (0/16 versus 4/10, p = 0.04) and cough (4/16 versus 9/10, p = 0.002) than CRA vaccinees with a confirmed intercurrent viral infection. Recipients of TI vaccine and Pl(i.m.) did not develop reactions at the injection site. For each of the CRA vaccines tested, a dominant CRA virus was identified. The dominant CRA viruses were isolated from a greater number of infants or for a longer duration than the non-dominant CRA viruses. All 14 non-dominant CRA viruses were recovered from infants within the first week after vaccination; 24 of 77 dominant CRA viruses were recovered more than 7 days after vaccination. The immunogenicity of CRA vaccines was not affected by, a confirmed intercurrent viral infection or low titres of influenza-specific antibody. However, interference was observed between the CRA viruses in the bivalent CRA vaccines. Immunogenicity of TI vaccine may have been affected by low titres of influenza-specific antibody.