The Chelyabinsk Region (Southern Urals) is high endemic territory. The TBE incidence is 3.57 ± 1.7 per 100 000 of population. A level of vaccination against TBE increased from 0.3 to 34.8% in 1999 - 2013. Specific immunity of population in 35.9% is connected with vaccination, in 64.1% with natural immunity consequently latent contact with TBE virus. Dynamics of vaccinal prevention, increasing of population immunity in different landscapes, and in different age groups were studied. 77.7% of TBE patients did not vaccinated, 18.2% received of specific immunoglobulin at postexposition and 3.7% persons were vaccinated. Unusual lethal case in patient, who received 8 doses of vaccine is analysed in this article.

Vaccination remains the only way to prevent tick-borne encephalitis (TBE). All TBE vaccines are based on strains of the Far Eastern and European subtypes of TBE virus. Currently, the Siberian subtype of the virus, which differs from the vaccine strains, accounts for 80–100% of the genetic population of TBE virus in most of Russia. The proportion of TBE vaccinated patients among those infected was different from year to year in Russia, e.g. 3.9% in 2012 and 1.5% in 2018, there were also some fatal cases registered among vaccinated patients. In this regard, evaluation of the effectiveness of vaccination against various genetic subtypes of TBE is a promising area of research. The purpose of this study was to summarise the results of studies investigating effectiveness of specific prevention of TBE as regards various genetic subtypes of the virus. The paper analyses data on the effectiveness of TBE vaccination in experimental settings and in real life. It was demonstrated that the use of vaccines for prevention of TBE is effective, provided the vaccination coverage is not less than 80%. The paper cites the data from a long-term study of the stability and protective activity of vaccine immunity against TBE virus strains isolated in highly endemic territories. It was established that TBE vaccines have high immunogenic activity and contribute to the production of stable protective antibodies against the strains of the three genetic subtypes of the virus. Protective efficacy of vaccination depends on the number of vaccinations received, the vaccination scheme, gender and age of those vaccinated. The paper concludes by saying that further studies are needed to assess TBE vaccine efficacy in order to improve vaccination tactics, to better understand causes of morbidity and mortality among vaccinated individuals.

Relevance.Modern inactivated culture vaccines against tick-borne encephalitis (TBE) with at least 70% of the population living in the  natural foci of the FE give a high epidemiological effect. Unresolved  issues are the simplification of the cumbersome vaccination scheme,  the optimal number of revaccinations, the protective titer of  antibodies against the Siberian subtype of the TBE virus dominant in Russia.Goalof this work is to study the state of postvaccinal immunity in the population of the highly endemic area of the Trans-Urals.Materials and methods. 1381 blood serum of the population vaccinated from 3 to 13 times with vaccines was studied: unconcentrated culture inactivated from strain No. 205 of the TBE  virus produced by «Virion», Tomsk, «EnceVir» produced by  «Microgen», Tomsk, produced by Chumakov Federal Scientific Center for Research and Development of Immuneand-Biological Products of  Russian.To identify specific antibodies – IgG, IgM, antigen of TBE  virus, sets of reagents of ELISA from «Vector-Best» were used.  Neutralizing activity of sera was determined by the index of  neutralization index with 4 strains of the Siberian subtype of TBE  virus.Results.The immune layer among the vaccinated population in 10 districts of the Kurgan region, which differ in epidemiological tension, ranges from 69.9% to 94.6%. The intensity of humoral immunity  varied according to IgG titers in ELISA from 1: 100 – 1: 200 to 1:  3200 (rarely 1: 6400). The duration and intensity of immunity  depends on the number of vaccinations and the number of missed  remote revaccinations. Preservation and intensity of immunity with  reliability P = 95%, higher in persons vaccinated 6–10 times  compared with the group of vaccinated 3 times. In persons who had 4–8 booster dose of vaccine, the immunity persisted for 15–19–36 years with an IgG titer of not more than 1: 100. The neutralizing  activity of the sera of vaccinated individuals with antibody titers from 1:100 to 1: 6400 was studied for the Siberian subtype of BCE. The  degree of protection of the vaccinated population against the doses  of the virus found in individual mites is determined. From the doses  of the virus, 57% of the vaccinated population are most often found  in mites, and from the dose of 105– 8%. Recommendations are  proposed on the tactics of revaccination of the population, depending on the level of immunity.

Tick-borne encephalitis (TBE) is a disease mainly affecting the central nervous system, serious medical and social problem in Russia and many European countries. TBE virus (TBEV) genetically divided into three major subtypes: the Far Eastern, European and Siberian. Siberian subtype of TBEV dominates in most part of Russia outside of the Far East. Modern cultural inactivated vaccine of domestic and foreign production prepared from the strains of the Far Eastern and European subtypes. In a review of the literature and our own researches are shown: the dominance of Siberian subtype (TBE) and data of vaccine-prevention. The importance of genetic differences between the Siberian subtype strains and vaccines strains are analyzed as well new approaches of the test strain selection.

Relevance. Vaccination against the tick-borne encephalitis (TBE), during the mass immunization, by using modern vaccines provides high epidemiological effect (98–99%); however, there are known cases of incidents among vaccinated population. The problem of incidents among vaccinated population is insufficiently studied, likewise a reliability of the diagnostic, vaccination conditions and causes of vaccinated people’s morbidity.Purpose of the article generalization of the information about morbidity among the vaccinated population.Conclusions. The review for the first time provides information about the main issues of this problem: the frequency of illness of vaccinated people in Russia (by federal districts and individual regions), disease development conditions, tied up with vaccination regimens and types of vaccines, clinical features and diagnosis of the disease of vaccinated people. Particular attention is paid to the state of post-vaccination immunity. The significance of two phenomena is being studied: incomplete neutralization of the virus, which leads to the formation of a fraction of a free infectious virus; and the phenomenon of the hyperimmunization with the development of immunological tolerance.