Safety and Immunogenicity of Inactivated Influenza Virus Vaccine Among Healthy Children 6-12 Weeks of Age

Methods: A double-blind, randomized, placebo-controlled trial was conducted in 1375 healthy US infants 6-12 weeks of age. Subjects received either 2 doses of trivalent inactivated influenza vaccine (TIV, Fluzone®, sanofi pasteur 2005-6 pediatric formulation) (N=915) or placebo (N=460) 1 month apart, along with indicated concomitant vaccines. Solicited adverse events were collected for 7 days following each vaccination, unsolicited adverse events for 28 days, and serious adverse events for 6 months. Hemagglutination inhibition antibodies to all 3 vaccine strains were measured following the second TIV/placebo dose. Results: No significant differences were seen between TIV and placebo groups for any safety outcomes. Fever ≥38oC rectal within 3 days of vaccination was seen in 11.2% vs 11.7% of TIV vs placebo recipients. Serious adverse events within 28 days of vaccine/placebo were reported in 1.9% of TIV and 1.5% of placebo recipients; only one (hypersensitivity reaction in a TIV recipient) was considered vaccine-related. Significantly increased antibody responses (p\<0.001) were seen against all 3 strains in TIV recipients by titer ≥ 1:40 or geometric mean titer (GMT) (p\<0.001). Altogether, 50% of infants had antibody titers ≥ 1:40 for H1N1, 86% for H3N2, and 11% for B compared with 7%, 10%, and 0.3% in the placebo group. The reciprocal GMT for influenza recipients was 33, 95, and 11 for H1N1, H3N2, and B vs. 7, 9, and 5 for placebo recipients. Over 90% of infants who received TIV had antibody ≥ 1:40 for at least one vaccine strain and 49.6% for 2 strains, vs. 16.4% and 0.9% in the placebo group. Conclusions: TIV administered to young infants beginning at 6-12 weeks of age is safe and immunogenic.