Safety and immunogenicity of low and high doses of trivalent live cold-adapted influenza vaccine administered intranasally as drops or spray to healthy children.

The safety and immunogenicity of various doses of trivalent cold-adapted influenza vaccine (CAIV-T) administered intranasally by drops or spray to children aged 18-71 months was examined. CAIV-T containing A/Johannesburg/33/94 (H3N2), B/Panama/45/90, and A/Texas/36/91 (H1N1) was safe and well-tolerated. At the highest CAIV-T dose, 90%, 50%, and 16% of initially seronegative subjects seroconverted to the H3N2, B, and H1N1 antigens, respectively. The lower immunologic response to the H1N1 vaccine strain compared with the other strains was associated with a low frequency of H1N1 shedding. No statistically significant differences in reactogenicity or immunogenicity were detected between subjects who received CAIV-T by drops or spray. In conclusion, this CAIV-T was safe and induced acceptable immunologic responses to 2 of the 3 vaccine strains. Studies are needed to confirm previous observations that receipt of two doses of this vaccine results in immunologic responses that confer protection to all 3 circulating influenza virus strains.