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.