Seropersistence of tick-borne encephalitis antibodies, safety and booster response to FSME-IMMUN® 0.5 ml in adults aged 18-67 years

A clinical study was carried out to evaluate the persistence of tick-borne encephalitis (TBE) antibodies 2 and 3 years after a primary vaccination series (three-dose regimen), and to assess the antibody response to a booster vaccination with FSME-IMMUN®. Volunteers (N=347, 18–67 years) who had received 2 doses of either FSME-IMMUN® or Encepur® adults and a third vaccination with FSME-IMMUN® were enrolled. Seropositivity rates were assessed by ELISA and neutralization test (NT). After the primary series, seropositivity rates were 99.1% as determined by ELISA and 100% by NT, decreasing to 85% and 96.8% in the first 2 years and to 88.7% and 95.4% after 3 years. Following booster vaccination, 100% of subjects were seropositive. Age was the only variable with a significant influence on the probability of remaining TBE seropositive 2 or 3 years after the third vaccination. In subjects aged 18–50 years, the pre-booster seropositivity rate was higher (88.7% and 92.3% after 2 and 3 years, respectively) than in tho...