A phase 1-2 trial was conducted in 48 adults to study safety and immunogenicity of an inactivated poliovirus vaccine produced using Vero cells (IPV-Vero). Participants received 2 intramuscular injections with IPV-Vero (40-8-32 D-Ag units) 4 weeks apart. IPV-Vero was well tolerated, and induced strong antibody responses in all participants. At least an 8-fold titre rise against all 3 types of poliovirus was found within 1 week of the first vaccination, indicating a strong secondary response in primed individuals. Two days after the first vaccination, there was no indication for such a booster reaction. The second vaccination 4 weeks after the first dose did not further increase antibody levels, indicating that an immune plateau had been achieved after the first vaccination. The second vaccination was not reactogenic despite the presence of these high pre-vaccination antibody levels. We conclude that IPV-Vero is well tolerated and strongly immunogenic in adults. In pre-immune adults 1 dose is enough to induce an impressive booster reaction.