A non-adjuvanted whole-virus H1N1 pandemic vaccine is well tolerated and highly immunogenic in children and adolescents and induces substantial immunological memory

► Vero cell-derived whole-virus H1N1 vaccine was well tolerated, inducing low adverse reaction rates (overall fever rate: 6% after the first vaccination; 7% after the second vaccination) in children and adolescents. ► Two vaccinations with the 7.5 μg dose induced high seroprotection rates in all subjects ranging from 84.2% to 100%. ► Persistence of antibodies against the vaccine strain was demonstrated at 6 months (GMTs ranging from 65.6 to 212.8) and at 12 months (GMTs ranging from 33.6 to 124.1) after primary vaccination. ► Vaccination with a seasonal influenza vaccine induced a strong booster response to the A/California/07/2009 strain reaching 100% seroprotection in all age groups, with GMTs ranging from 640.0 to 886.3.