Vaccine coverage, herd immunity and occurrence of canine distemper from 1990-1996 in Finland.

Official vaccine sales statistics, the development of the young dog population and the takes of available vaccines were used to calculate the vaccine coverage and herd immunity (HI) against canine distemper, endemic during 1990-1993 and epidemic in 1994-1995 in Finland. Despite the satisfactory vaccine coverage, HI was no more than 50-65% in 1990-1993 because low-take vaccines dominated the market. Replacement of the low-take with high-take vaccines in 1995 raised the HI to 90%, which coincided with the ending of the epidemic. In 1996, the HI was slightly above 70%, which was sufficient to control the disease despite infectious pressure caused by repeated imports.