Sustained antibody persistence for at least 15years after a booster vaccination against tick-borne encephalitis following different primary vaccination schedules: Third 5-year follow-up.

Abstract

Vaccination is the best mode of protection against tick-borne encephalitis (TBE) and its sequelae. The duration of protection and the optimal interval of repeat booster doses are still debated. The current study evaluated the persistence of the antibody response 11-15years after a first booster vaccination following different primary vaccination schedules with a TBE vaccine (Encepur Adults, manufactured by Bavarian Nordic, previously by GSK). This phase IV, open-label, mono-centric extension study enrolled adults who had received (at≥12years of age) primary vaccination with one of three randomly assigned TBE vaccine schedules (rapid [group R], conventional [group C], or accelerated conventional schedule [group A]) followed by a booster dose 3years later. The antibody response was measured annually from 11 to 15years post-booster using a TBE virus neutralization test (NT). An NT titer of≥10 was considered as a clinically meaningful threshold and surrogate for protection. In total, 194 participants were enrolled and included in the per-protocol set; 188 completed the study. The percentage of participants with an NT titer≥10 was 100% in group R and 99.0% in group A at all visits and ranged from 100% (year 11) to 95.8% (year 15) in group C. NT geometric mean titers were similar in the three study groups (181-267 in group R, 142-227 in group C, 141-209 in group A). NT geometric mean titers also remained high among participants≥50years old (98-206) and≥60years old (91-191) across study groups and time points. This study showed neutralizing antibody persistence for at least 15years after a first booster dose of the Encepur Adults TBE vaccine in all age groups evaluated, regardless of which primary vaccination schedule was given to adolescents or adults. Trialregistry: ClinicalTrials.gov: NCT03294135.