Pre-vaccination immunity and immune responses to a cell culture-derived whole-virus H1N1 vaccine are similar to a seasonal influenza vaccine

► Vero cell-derived whole-virus H1N1 vaccine is safe and immunogenic in young and older adults. ► All EU immunological licensing thresholds met in both populations by a single 7.5 μg dose. ► Vaccine-induced HI antibodies persisted for ≥6 months post-vaccination. ► Higher baseline seroprotection rates associated with 2008-09 or 2009-10 seasonal influenza vaccination. ► High baseline titers were probably associated with exposure to H1N1 circulating from 2000 to 2007.