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Lethal cases of tick-borne encephalitis in previously vaccinated patients have not been described. Modern inactivated vaccines against Tick-borne encephalitis (TBE) are high effective. The TBE cases, preference unfocal forms, are developed in persons with incomplete irregular vaccination. First case of lethal TBE after plural vaccination was described in the Kurgan region, the second case - in the Chelyabinsk region. These very rare unusual cases were studied. Being dominant the Siberian subtype of TBE virus is related with lethal TBE cases in the Chelyabinsk region. Unusual TBE case was developed in patient who had been vaccinated 8 limes with vaccines produced from strains of Far-Eastern TBE subtype («Virion», Tomsk, Chumakov institute, Moscow) and European TBE subtype (Encepur; FSME-Immun). Two years after the last vaccination a focal form of TBE was developed with lethal outcome at 9 th day. Specific antibodies IgM and IgG seroconversion were detected. The TBE virus antigen was detected in brain neurons by immunofluorescent test. Destructed neurons and gliocyles were shown by hystological study in cerebral hemispheres and cerebellum. The Purkinje cells were destructed. Possible reasons of surmounting vaccinal immunity including a genetic difference of vaccine and infection virus strains are discussed.

In the Yaroslavl region (Central Federal District of Russia), endemic of tick-borne encephalitis (TBE), the features of epidemiology of this infection were studied during 1992-2012. Cyclical fluctuations in the incidence of TBE, the lack of the trend to decrease of the incidence were observed, the average annual incidence was 1,6 ± 0,32 per 100 thousand ofpopulation. The prevalence offebrile forms of disease was 62,2%, meningeal forms - 16,3%, the total percentage offocal forms was 13,9%. Manifestations of evolution of TBE were: the increase of the epidemiological significance of anthropogenically transformed natural foci, anthropurgical foci of TBE, until 81% of TBE cases were unvaccinated citizens, the high lethality of 4% and the high frequency of cases of alimentary infection of TBE of 7,8% with lethality of 10,8%. The aethiological agent of 10 lethal cases was Siberian subtype of TBE virus.