Analysis of delayed TBE-vaccine booster after primary vaccination.

An open, uncontrolled single centre study was conducted in the Travel Clinic at the Military Hospital, Brussels. Eighty-eight subjects were recruited who had a primary series of tick-borne encephalitis (TBE) vaccine more than 5 years ago and who never received a booster dose afterwards. Response rate after booster vaccination was very high: 84 out of 88 subjects (95.5%) had neutralizing antibodies on plaque reduction neutralization test and all (100%) had IgG antibodies on ELISA, on Day 21-28 after booster vaccination. This study adds valuable information to the common situation of delayed booster interval. The results of our study indicate that in young healthy travellers (<50 years), one booster vaccination after a primary series of TBE vaccine in the past is sufficient to obtain protective antibodies, even if primary vaccination is much longer than the recommended booster interval of 5 years.