Seroimmunity to poliomyelitis in Sweden after the use of inactivated poliovirus vaccine for 10 years.

This study was undertaken in 1968 in collaboration with the World Health Organization as part of a co-operative evaluation of vaccination programmes. The situation in Sweden was of particular interest as only inactivated vaccines had been used for immunization against poliomyelitis. The WHO programme includes evaluation of both seroimmunity and resistance to poliovirus infection but the present report concerns only the serological studies.About 3 000 people, selected on a statistical basis as being a representative sample of the Swedish population, were sent questionnaires concerning their vaccinations against poliomyelitis. Answers were returned by 90% of the sample population and blood samples were collected from 2 294 persons. More than 95% of subjects under 30 years of age had received 2 or more injections, but the proportion of vaccinated individuals decreased slightly among people over 30 years of age. In the oldest age group questioned (60-70 years) only 20% had been vaccinated. Antibodies to the 3 types of poliovirus were present in more than 95% of the sera in all age groups except two. Samples seronegative to one or more types of virus were found in about 15% of people in the oldest age group and among children vaccinated during the first years of poliovirus vaccination (1957-61).