EPIDEMIC TYPE A INFLUENZA IN SOUTHWESTERN ONTARIO IN 1963.

From February to April 1963 epidemic type A influenza occurred in Southwestern Ontario. Eighty cases were diagnosed virologically, 24 of them by isolation of virus. The epidemic strain of virus proved unusually difficult to adapt to growth in embryonated eggs, and it had low avidity for antisera. Antigenically it differed from A2 strains of earlier years and belonged to the subgroup of A2 influenza viruses characterized by the A2/Japan/170/62 strain. Antisera to A2 strains of earlier years neutralized the present strain, but antisera to the present strain failed to neutralize the earlier viruses. Some patients formed antibodies to the present epidemic strain alone, and others formed antibodies both to this strain and to earlier A2 strains.