Elimination of poliomyelitis in Finland.

In Finland paralytic poliomyelitis has disappeared after immunization programs carried out exclusively with inactivated poliovirus vaccine (IPV). A sharp decrease in the number of patients with poliomyelitis occurred after mass vaccination in 1960-1961, when 51% of the population had received the complete primary vaccination. Immunity is maintained by continuous vaccination of infants, whose vaccination rate is close to 98%. Intensive poliovirus surveillance in 1972-1974 revealed that dissemination of the virus has also virtually ceased. Serologic surveys indicate that greater than or equal to 90% of individuals older than 15 years of age possess antibodies to all viral types, but in the younger age groups the proportion with antibodies to types 1 and 3 is lower, a finding that is alarming, especially in the case of type 3. Revaccination of seronegative children and conscripts has induced rapid booster-like responses, indicating that fully vaccinated individuals, although without demonstrable antibodies, are protected against poliomyelitis. The new, improved IPV developed in Holland induces satisfactory antibody titers in all vaccinees, with two injections--or perhaps even one--leading to long-lasting immunity.