Outbreak of poliomyelitis in Finland in 1984. Description of nine cases with persisting paralysis.

Finland has been free of poliomyelitis since 1964 following a high coverage regular immunization programme using the Salk-type trivalent inactivated poliovirus vaccine. In late 1984 an outbreak of poliomyelitis with widespread circulation of poliovirus type 3 throughout the country was found. A thorough surveillance revealed 9 sporadic cases with acute persisting paralysis, all shown to be caused by poliovirus type 3. The preceding 20-year period free from poliomyelitis contributed to some diagnostic problems.