Long-term immunity following vaccination with killed poliovirus vaccine in Sweden, a country with no circulating poliovirus.

The long-term immunity following vaccination with killed poliovirus vaccine was analyzed by making repeated antibody surveys. A comparison between the levels of antibody of vaccinated groups of children and young adults in 1968 and 1978 indicated that mean levels of antibody of the age groups that, during the period 1968-1978, had not received any extra booster differed by less than or equal to 0.3 log10. Children born in the period 1964-1967 and young adults born in the period 1960-1963 were compared in 1978. The two groups had received their last booster an average of six and 10 years ago, respectively. The mean level of antibody in the older group, which had received booster approximately 11 years previously, was 0.2 log10 lower against type 1 poliovirus and 0.1 log10 lower against type 3 virus than the corresponding titers of the younger children who had received booster approximately six years earlier. The levels of antibody to poliovirus type 2 were identical in both age groups.