After the catch-up vaccination, all except one of the 125 subjects reached an antibody level of ≥25 U/ml, corresponding to a putative overall seroprotection rate of 99.2% irrespective of buy FG-4592 the number of previous vaccinations (Table 3c). The GMC fold increases are strongly dependent on the number of previous vaccinations (Fig. 2). In

adults of both age groups the highest fold increase was observed in subjects with 2 previous vaccinations (14.8-fold in the young adults and 17.1-fold in the elderly), followed by those with only 1 previous vaccination (9.1-fold in young adults and 8.3-fold in the elderly). After 3 or more vaccinations, the fold increase drops to about 4–6 (range: 3.7-fold to 5.8-fold). Due to the small sample size no such analysis was done for children. Altogether 6 adverse reactions, 5 in adults and 1 in children/adolescents, were reported in temporal relationship with the catch-up vaccination during the study: Of the adverse reactions observed in adults, 3 were local reactions at the injection site, 1 was a systemic reaction PDGFR inhibitor with flu-like symptoms with onset 2–3 days after immunization, and 1 was a

combination of a local reaction and flu-like symptoms 12 h after immunization. The adverse reaction in the pediatric population was a local reaction at the injection site. All 6 adverse reactions were classified the as non-serious and labeled in the summary of product characteristics. The incidence was 0.48% overall, thereof 0.45% in the adult subpopulation and 0.80% in the pediatric subpopulation. With 1115 adult and 125 pediatric subjects analyzed, this is the largest study on incomplete and/or irregular TBE vaccination schedules conducted so far and the first study which also included children. The results presented here clearly demonstrate that a catch-up vaccination with a single dose of FSME-IMMUN was able to elicit high antibody levels in most of the previously irregularly TBE vaccinated subjects over a broad age range. This finding is corroborated by a recently published study where FSME-IMMUN was administered

in healthy young adults with regular or delayed TBE vaccination histories and substantial booster responses were noted in the majority of subjects [10]. However, whereas our study clearly indicates that the antibody response to a further dose of TBE vaccine correlates with the number of previous TBE vaccinations, the booster responses in the study conducted by Askling et al. were independent of the number of previous doses. This discrepancy could be explained by differences in the study design and/or the small sample size of various vaccination subgroups in the study of Askling et al. In our study, putatively seroprotective anti-TBE antibody levels (≥25 U/ml) in response to the catch-up vaccination were reached by 99–100.