TBE vaccination and the Austrian experience

Abstract

In the pre-vaccination era, Austria had the highest recorded morbidity of tick-borne encephalitis (TBE) in Europe. The disease accounted for more than 50% of all viral meningoencephalitides in the eastern and southern parts of the country. This prompted us to start a cooperative vaccine development project in 1971 with J. Keppie from the Microbiological Research Establishment, Porton Down, England. After very satisfactory results of field studies, conducted in individuals for whom TBE was classified as occupational disease (forest workers, farmers, etc.), the killed virus vaccine (see chapter by N. Barrett in this issue), was made commercially available by Immuno AG Vienna (now Baxter Health-Care). The vaccine proved to be highly immunogenic and very well tolerated in both adults and children. After completing the series of three vaccinations seroconversion rates of >99% were recorded. In Austria, as in other European countries, TBE is now acquired for the most part during leisure activities. In view of this fact a mass vaccination campaign was initiated in 1981. Subsequently, the vaccination coverage of the Austrian population increased from 6% in 1980 to 86% in 2001, exceeding 90% in some of the high-risk areas. Data annually collected by our surveillance system show that the clinical effectiveness of the vaccine is excellent. Based on the assumption that the whole Austrian population is at risk of infection the calculated rate of protection after three doses of the vaccine is 96-98.7%. Breakthrough disease is rare and affects mainly higher age groups. Since the advent of TBE vaccination only one single case has been observed in the age group up to 20. The increasing vaccination coverage led to a more or less steady decline of TBE, drastically reducing the public health problem that the disease poses in Austria, especially in the provinces, where formerly the highest morbidity rates were observed. For example, in Carinthia, in the years 1973-1982 an average annual incidence of 155 was recorded, compared with only four annual cases in the last 4 years. The Austrian experience shows that containment of a tick-borne viral disease is feasible, provided a well-tolerated and effective vaccine is available that is widely accepted by the general population.