EFFICACY OF VACCINATION AGAINST TICK-BORNE ENCEPHALITIS (TBE)

Abstract

Since 1973, blood samples were 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 2 doses given 1-3 mo. apart and a 3rd dose injected 9-12 mo. later. This resulted in a seroconversion rate of 96% (n = 444) in the hemagglutination-inhibition (HI) test and of 99% in the ELISA [enzyme-linked immunosorbent assay]. The vaccine induced high titers of complement-fixing antibodies. Antibody formation did not depend significantly on the age of the vaccinees. After 3 yr, 66% (n = 321) of those vaccinated still possessed antibodies in the HI test and 87% in the ELISA. Antibodies were found in the sera of some persons at the end of the observation period (i.e., 6 yr). Persons who became seronegative still responded positively to a booster dose of vaccine. Thus, the intervals between injection of the single doses of vaccine can be extended considerably without jeopardizing the success of vaccination. The protection is > 99%.