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Tick-borne encephalitis (TBE), a zoonotic arbovirus infection, poses a significant health problem in western and central Europe, as well as many parts of Asia [1]. To protect against TBE, two vaccines are distributed internationally in TBE-endemic countries: Encepur ® (Novartis Vaccines, Germany) and FSME-Immun® (Baxter, Austria). Both TBE vaccines contain inactivated whole-virus antigens, adsorbed to the adjuvant aluminum hydroxide. The primary vaccination course for both vaccines consists of three intramuscular injections, the first being administered on day 0, the second 1-3 months later and the third 9-12 months after the second. In the case of FSME-Immun, an abbreviated conventional vaccination schedule has recently been licensed, in which the second dose is injected 2 weeks after the first, and the third is given after 6 months [2,3]. For Encepur, a rapid immunization schedule was developed in the early 1990s for use at short notice with injections on days 0, 7 and 21 [4].
The vaccines are based on either the TBE-virus strain Neudörfl (marketed version of FSME-Immun, Baxter), or strain K23 (marketed version of Encepur, Novartis Vaccines). Over the last 20 years, a number of modifications have been made to the pharmaceutical composition of both vaccines, which were subsequently renamed. The predecessor of Encepur was FSME Vakzine Behring ® , which contained polygeline as a stabilizer [4]. Earlier preparations of FSME-Immun contained thiomersal as a preservative [5]. These and a number of other modifications of the pharmaceutical composition had no effect on the immunogenicity of the vaccines, as a result the modified versions of FSME-Immun and Encepur can each be regarded as a different version of the respective predecessor vaccine [5,6]. To date, good clinical practices of controlled clinical studies on the ability to booster the immune response by Encepur 'new version'after primary immunization with Encepur 'old version'have been carried out and have been published. Sequencing of the viral genome revealed a high level of homology between the TBE strains Neudörfl and K23, with only a few base exchanges within the glycoprotein gene, whose product induces cross-neutralizing antibodies [7]. However, Encepur and FSME-Immun -independant from their individual version -are two different vaccines. There are differences in the production process (not all of the details are available to the public), in the amount of antigen...