Immunogenicity, large scale safety and lot consistency of an intradermal influenza vaccine in adults aged 18-60 years: Randomized, controlled, phase III trial.

Background: Vaccination is the most effective way of reducing the large health and economic burden of influenza, yet vaccination coverage remains low, particularly among non-elderly adults. Intradermal influenza vaccine produce an effective immune response and represents an alternative to intramuscular influenza vaccination.

Results: The three industrial lots of intradermal vaccine were equivalent in terms of post-vaccination titres elicited by day 21. The intradermal and intramuscular vaccines induced similar post-vaccination titres, and satisfied all three immunogenicity criteria set out in the European regulatory guidelines for influenza vaccines for each of the three influenza strains. The solicited systemic reaction profile and the incidence and type of spontaneously reported adverse events were similar in the two vaccine groups and in line with the known safety profile of inactivated influenza vaccines. Injection site reactions were more frequent with intradermal vaccination.

Methods: A Phase III multicentre, randomised, controlled, double-blind (for the three different lots of intradermal vaccine) study assessed lot-to-lot consistency, immunogenicity and safety of an intradermal inactivated trivalent splitvirion influenza vaccine in 2,255 adults aged 18-60 years. Participants received one of three lots of intradermal vaccine containing 9 microg of haemagglutinin per influenza strain, or a licensed intramuscular control vaccine containing 15 microg haemagglutinin/strain.

Conclusions: This intradermal vaccine containing 9 microg per influenza strain, provides an alternative to conventional intramuscular vaccination, has a reliable production method and is equally immunogenic and well tolerated in adults. The study was registered at clinicaltrials.gov (identifier NCT00383539).