Five year follow-up after a first booster vaccination against tick-borne encephalitis following different primary vaccination schedules demonstrates long-term antibody persistence and safety

Long-term vaccination programs are recommended for individuals living in regions endemic for tick-borne encephalitis (TBE). Current recommendations suggest a first booster vaccine be administered 3 years after a conventional regimen or 12–18 months after a rapid regimen. However, the research supporting subsequent booster intervals is limited. The aim of this study was thus to evaluate the long-term persistence of TBE antibodies in adults and adolescents after a first booster dose with Encepur^®. A total of 323 subjects aged 15 years and over, who had received one of four different primary TBE vaccination series in a parent study, participated in this follow-up Phase IV trial. Immunogenicity and safety were assessed for up to five years after a first booster dose, which was administered three years after completion of the primary series. One subset of subjects was excluded from the booster vaccination since they had already received their booster prior to enrolment. For comparison, immune responses were still recorded for these subjects on Day 0 and on an annual basis until Year 5, but safety information was not collected. Following a booster vaccination, high antibody titers were recorded in all groups throughout the study. Neutralization test (NT) titers of ≥10 were noted in at least 94% of subjects at every time point post-booster (on Day 21 and through Years 1–5). These results demonstrated that a first booster vaccination following any primary immunization schedule results in high and long-lasting (>5 years) immune responses. These data lend support to the current belief that subsequent TBE booster intervals could be extended from the current recommendation. NCT00387634.