Background: Improved influenza vaccine strategies for infants and preschool children are a high priority.
Methods: The immunological response and safety of a thimerosal-free trivalent inactivated influenza vaccine at 2 different doses (0.50 mL vs 0.25 mL) was evaluated in children aged 6-35 months. The study was randomized, observer blind, multicenter, and stratified by age (6-23 months and 24-35 months), and it accounted for prior influenza immunization status.
Results: Three hundred seventy-four children were in the total vaccinated cohort (study vaccine 0.25-mL dose, n = 164; 0.50-mL dose, n = 167; comparator 0.25 mL, n = 43). Regulatory criteria for immunogenicity of influenza vaccines in adults were met for all virus strains and doses for both age strata. A modest but not statistically significant improvement in immune responses was observed with the higher dose and reactogenicity, and safety of the 2 doses was not significantly different.
Conclusions: The 0.5-mL dose of the study vaccine, when administered to children aged 6-35 months, resulted in a modest but not statistically significant improvement in immunogenicity with clinically similar safety and reactogenicity compared with the 0.25-mL dose. Further studies comparing full- and half-dose influenza vaccine in young children are needed.
Clinical trials registration: NCT00778895.
© The Author 2012. Published by Oxford University Press on behalf of the Pediatric Infectious Diseases Society.