Immunogenicity and reactogenicity of a highly purified vaccine against tick-borne encephalitis

Immunogenicity and reactogenicity of a vaccine containing inactivated tick-borne encephalitis virus prepared by continuous flow zonal ultracentrifugation were compared with those of a previously used, less purified vaccine. Antibody response as measured by hemagglutination inhibition (HI) and enzyme-linked immunosorbent assay (ELISA) was 93% after two vaccinations and 100% after a third dose. The zonally purified vaccine impressively reduced the incidence of side reactions. Pyrexia (greater than 37.3 degrees C) was recorded in only 4--10% of the vaccinees almost exclusively after first vaccinations compared to 17--68% with the old type of vaccine. When these results are evaluated according to criteria commonly used in the United States (ie, pyrexia greater than 100 degrees F = 37.8 degrees C), almost no fewer would be recorded. The frequency of systemic side reactions was even lower (statistically significant) after second and third vaccination. This highly purified vaccine therefore represents an effective and well-tolerated means for the immunoprophylaxis of TBE.