Long-term persistence of tick-borne encephalitis antibodies in adults 5 years after booster vaccination with Encepur Adults.

Tick-borne encephalitis (TBE) is a potentially serious disease, especially in adults. There is no treatment available for TBE; supportive therapy may help to ease symptoms of the disease. Vaccination is the most effective method of preventing TBE disease and is recommended for those who live, work, or travel in TBE-endemic areas. Regular booster vaccinations are recommended every 3-5 years to maintain protection. Evidence from recent clinical studies suggests that TBE antibodies persist at high levels for longer than the current recommended intervals for TBE booster vaccination. The aim of this study was to evaluate the long-term persistence of TBE antibodies in adults after primary vaccination using a rapid schedule and a first booster dose of Encepur Adults, an inactivated TBE vaccine. A total of 222 adults 19-51 years of age were invited for serological follow-up investigations 3 and 5 years following their first booster dose. High antibody titres were recorded throughout the follow-up period. Neutralization test (NT) titres > or =10 were noted in 99% of subjects 3 and 5 years after the first booster vaccination and 97% tested positive by enzyme-linked immunosorbent assay (ELISA). These results indicate that initially high levels of TBE antibodies following the first booster dose of the vaccine may lead to long-term persistence of TBE antibodies, confirming previous findings and suggesting it may be appropriate to extend the interval between booster doses from 3 to 5 years.

TBE booster immunization according to the rapid immunization schedule: are 3-year booster intervals really necessary?

In order to evaluate the need for further booster immunizations, 222 subjects aged 20-52 years, who had received the first booster dose with a new tick-borne encephalitis (TBE) vaccine in a preceding study, were invited for a serological follow-up. A total of 191 and 182 adult subjects were analyzed for the persistence of neutralizing TBE antibodies at 1 and 2 years following the first booster immunization, respectively. Both serological follow-ups revealed high levels of neutralizing TBE antibodies in more than 99% of subjects. Although an expected decline of the respective geometric mean titers (GMTs) was noted after booster immunization, the titers were still far above the values noted after primary immunization at the 2-year follow-up. The kinetic curve clearly indicates a longer persistence of neutralizing TBE antibodies than currently expected. To conclude, these results suggest that the administration of a further booster dose 3 years after the first one (according to current recommendations) does not seem to be necessary in this study population.

Kinetics of the immune response after primary and booster immunization against tick-borne encephalitis (TBE) in adults using the rapid immunization schedule.

UNLABELLED: A total of 222 adult subjects aged 19-51 years were enrolled in this multi-center, phase III study to evaluate immunogenicity and safety of the first booster immunization with a new tick-borne encephalitis (TBE) vaccine. This was an extension study that followed subjects who had received primary immunization 12-18 months previously with either the new or formerly licensed TBE vaccine according to the rapid immunization schedule (i.e. on Days 0, 7 and 21). Compared to the levels of primary immunization, prior to first booster, neutralizing TBE antibodies (geometric mean titers, GMTs) of both vaccination groups had remained on a high level and were far above the detection limit of the neutralization test used. All subjects showed a sharp increase of TBE antibodies following the booster. The booster was well tolerated by the subjects. CONCLUSION: These results in terms of both immunogenicity and safety indicate that the TBE vaccination with this new TBE vaccine can be used effectively and safely in adults. A long lasting immunity can be concluded from the strong immune response following the first booster.