A randomized clinical trial to identify the optimal antigen and MF59® adjuvant dose of a monovalent A/H1N1 pandemic influenza vaccine in healthy adult and elderly subjects

► One dose of 7.5 μg influenza vaccine induced optimal antibody responses and long-term protection. ► Single 7.5 and 3.75 μg doses met licensure criteria in elderly and adults, respectively. ► Good booster response one year after one-dose priming schedule.