Comparison of Half and Full Doses of an MF59-Adjuvanted Cell Culture-Derived A/H1N1v Vaccine in Japanese Children

Introduction: The substantial pandemic (A/H1N1v) influenza disease burden in children highlights the need for effective vaccination. We report the results of modern cell culture technology, lower doses of antigen, and different doses of MF59 (R) adjuvant (Novartis Vaccines, Marburg, Germany), on the immunogenicity and safety profile in a healthy Japanese pediatric population. Methods: A total of 123 children from 6 months to 19 years of age were randomly assigned in a 1: 1 ratio to receive, at 21-day intervals, two doses of either 3.75 mu g antigen with 50% of the standard MF59 dose (group A) or 7.5 mu g antigen and 100% standard MF59 dose (group B). Antibody levels were measured by hemagglutinin inhibition (HI) and microneutralization assays on day 1 and on days 22 and 43 (3 weeks after the first and second vaccinations, respectively). Solicited adverse events were reported for 7 days after each injection and spontaneous events were reported throughout the study period. Results: At 3 weeks after the first vaccination, seroprotective HI antibodies (titers >= 40) were observed in 56% and 78% of subjects from groups A and B, respectively; 100% in both groups exhibited HI titers >= 40 after the second dose. The reactogenicity profile was acceptable, with local and systemic reactions described as mainly mild to moderate in severity. Five serious adverse events were reported, but none related to the study vaccine. Conclusion: One dose of cell culture-derived A/H1N1v vaccine containing 7.5 mu g antigen with the full MF59 adjuvant dose was immunogenic and well tolerated in healthy Japanese children, meeting all three European Union Committee for Medicinal Products for Human Use (EU CHMP) licensure criteria. Two doses of 3.75 mu g antigen with 50% of the standard MF59 dose fulfilled these licensure criteria.