[Efficacy of Vaccination Against Tick-Borne Encephalitis]

Since 1973 blood samples have been investigated at random for the presence of antibodies to tick-borne encephalitis (TBE) virus in persons vaccinated with the Austrian TBE vaccine. The immunization schedule was to doses given 1 to 3 months apart and a third dose injected 9 to 12 months later. This resulted in a seroconversion rate of 96% (n=444) in the haemagglutination-inhibition (HI) test and of 99% in the ELISA. The vaccine also induced high titres of complement-fixing anti-bodies. Antibody formation did not depend significantly on the age of the vaccinees. After three years, 66% (n=321) of those vaccinated still possessed antibodies in the HI test and 87% in the ELISA. Moreover, antibodies were still found in the sera of some persons at the end of the observation period (i.e. 6 years). Persons who had become seronegative still responded positively to a booster dose of vaccine. In a large number of persons it was evident that the intervals between injection of the single doses of vaccine can be extended considerably without jeopardizing the success of vaccination. The protection rate is larger than 99%.