Safety and immunogenicity of an inactivated thimerosal‐free influenza vaccine in infants and children

Objective  Few prospective studies of inactivated split virion influenza vaccine have been conducted in infants and children. Our objective was to evaluate the safety, reactogenicity and immunogenicity of a thimerosal‐free inactivated influenza vaccine (Fluvax ® ; CSL Limited, Parkville, Australia) in children aged 6 months to <9 years. Methods  A prospective, open‐label, phase III clinical trial was conducted in 298 healthy children previously unvaccinated with influenza, commencing in the Southern Hemisphere 2005 autumn. Participants were divided into two groups (Group A: ≥6 months to <3 years; Group B: ≥3 years to <9 years), and received two doses of the 2005 vaccine, and one dose of the 2006 vaccine one year later (Group A: 0·25 ml per dose; Group B: 0·5 ml per dose). Vaccine safety and reactogenicity was evaluated for 30 days after each dose. Immunogenicity was assessed using hemagglutination inhibition and single radial hemolysis assays. Results  There were no withdrawals due to adverse events (AEs). The majority of solicited local and systemic AEs were of mild severity. A maximum intensity of severe was reported for injection site pain and fever by only 3·0% and 3·4% of participants, respectively. The vaccine was immunogenic for all antigens, with ≥95% of both younger and older children achieving seroprotection after dose 2. Conclusions  This thimerosal‐free inactivated influenza vaccine had a favorable safety profile and was immunogenic in children aged ≥6 months and <9 years. Primary and booster vaccination produced consistently immunogenic responses including in children under 3 years of age receiving 0·25 ml doses of vaccine.