[Field studies with a new tick-borne encephalitis (TBE) vaccine].

The vaccine used contained formalin-inactivated TBE virus that was grown in chick embryo cells and adsorbed to Alhydrogel. In a first study, conducted in 1973, a total of 81 volunteers were given subcutaneously two doses of vaccine 4 weeks apart, and a third dose 7-9 months later. After each vaccination, the rates of seroconversion were assayed in the hemagglutination inhibition test. The values obtained were 76%, 96% and 98%, respectively. The geometric mean titers found were 1:26, 1:36 and 1:44. The vaccine was well tolerated locally and systematic reactions such as fever headache and fatigue were only recorded after the first dose of vaccine. In 1974 and 1975 a total of 30,000 persons were vaccinated in areas where the disease is endemic. Most of the vaccinees work in forests and are, therefore, at high risk of infection. Circumstantial evidence indicates that the vaccine is protective.