The immunogenicity and safety of a single 0.5 mL dose of virosomal subunit influenza vaccine administered to unprimed children aged ≥6 to <36 months: data from a randomized, Phase III study.

This study evaluated the immunogenicity, safety and tolerability of a single 0.5 mL dose of the seasonal virosomal subunit influenza vaccine (Inflexal V, Crucell, Switzerland) in 205 healthy, unprimed children aged at least 6 to <36 months, evaluated at four weeks post-vaccination and seven months from baseline. Of the enrolled children, 102 received one single 0.5 mL dose and 103 received the standard two 0.25 mL doses given four weeks apart. Both treatments evoked an immune response that satisfied the EMA/CHMP criteria for yearly vaccine licensing for all three vaccine strains. Exploratory analyses revealed no differences between the groups at four weeks post-vaccination. Furthermore, immunogenicity was maintained seven months after the first vaccination after both the 0.5 mL and standard two 0.25 mL doses. Adverse events were comparable between groups and were as expected according to the safety profile of the vaccine; overall, the vaccine was well tolerated. Our results show that a single 0.5 mL dose effectively and safely provided long-term immunogenicity to all three influenza strains in unprimed children aged at least 6 to <36 months.