Immunological classification of 25 European strains of poliomyelitis virus.

Twenty-five strains of poliomyelitis virus isolated from paralytic cases in the Netherlands, Belgium, and Germany were classified either by testing resistance of immunized monkeys, or by neutralization. Seventeen strains (68%) were classified as type 1, 7 (28%) as type 2, and 1 (4%) as type 3. Strains of type 2 are presumably present from year to year, only occasionally, however, causing paralytic poliomyelitis. Type 1 strains, on the contrary, are apparently the agents tending to cause epidemics of the paralytic disease.