ABSTRACT
In three areas of the Netherlands with a high incidence of swine fever all pigs over two weeks old were vaccinated with the so-called "Chinese" (C)-strain of vaccine virus. The mass vaccination at the start of each compaign was supplemented thereafter by vaccination of young stock at the age of 6 to 8 weeks and of all pigs introduced from outside. In one area vaccination was pursed for three years, and in two areas for one year. Vaccination was compulsory and supported by stamping out of affected herds and the application of the usual veterinary police measures. The number of outbreaks in the vaccinated areas declined from two weeks after the start of the campaign and clinical disease had diappeared after five months. During this period outbreaks related to vaccination were diagnosed in each area. Some outbreaks were due to vaccination procedures which probably caused the spread of virus from congenitally infected litters to susceptible piglets, which had lost maternal antibodies. Only one "vaccine break" was diagnosed. Outbreaks of swine fever, due to the presence of residual virus in the designated areas, have not been reported up to two years after vaccination was discontinued. The campaigns have shown that swine fever can be eradicated from enzootic areas by a strict vaccination regime pursued for one year.