Hepatitis A virus (HAV) RNA detection in Polish blood donors and likely transmissions through blood components during the 2017-2019 epidemic.

BACKGROUND: In Poland, hepatitis A virus (HAV) RNA screening was performed in plasma for fractionation usually immediately before shipment. OBJECTIVE: Our goal was to study epidemiology, rate of transfusion transmitted HAV during epidemic (2017-2019), and viral characteristics of infected plasma donors. STUDY DESIGN AND METHODS: HAV RNA was tested in 1,866,590 donations from 1,210,423 donors using RT-PCR in mini pools of 96 (MP96) or TMA in MP16. Virological characteristics included RNA level (RL), antibody testing, and sequencing. RESULTS: Twenty-one HAV infections were identified (1.13/100,000 donations; 95% confidence interval [95% CI]: 0.74-1.72) and (1.73/100,000 donors; 95% CI: 1.35-2.65). The Blood Transfusion Centers were also informed about three donors, who were hospitalized for hepatitis A soon after their blood donation. In addition, we identified a donor, who had reactive result for HAV after receiving HAV vaccination. He tested positive twice 10 days after receiving the first and the second dose. The highest RL was 16 million IU/ml, mean 1,706,905 IU/ml, and median 220 IU/ml. The longest detectable RL lasted for 113 days. HAV-infected donors were seronegative (36%) or IgM positive (64%). We followed up on 12 HAV contaminated blood components issued for transfusion. In two out of seven identified patients viral transmission was confirmed (28.6%). CONCLUSION: Based on our results, we propose a 6 month deferral after HAV infection and 14 days post HAV vaccination. The infectivity rate was below 30%. The HAV RNA testing could be considered as an additional safeguard against HAV transmission at the time of increased incidence of HAV infections in the general population.

Molecular diagnosis of COVID-19 ­ present experiences / Molekularna diagnostyka COVID-19 ­ dotychczasowe doswiadczenia.

Severe acute respiratory syndrome Coronavirus-2 (SARS-CoV-2), a new highly emerging and pathogenic for human RNA virus, is responsible for the present COVID-19 pandemic. Molecular diagnostic methods, including real-time reverse transcription-PCR (RT-PCR) assay are the recommended methods for the identification and laboratory confirmation of COVID-19 cases. RT-PCR allows for detection the RNA of the virus in clinical specimens from patients suspected of COVID-19 with high specificity and sensitivity. Testing is still crucial for rapid detection of infected persons, implementation of appropriate measures to suppress further virus transmission and mitigate its impact. In response to demand of a molecular diagnostic test for SARS-CoV-2, within a first few months ongoing pandemic many commercial kits has become available on the market. However, these tests have varied in number and type of molecular targets, time of reaction as well as quality. In this study we compared different commercial tests for the detection of SARS-CoV-2 in clinical samples sending to Laboratory of Department of Virology, NIPH-NIH.

Production of Sc medical radioisotopes with proton and deuteron beams.

Proton and deuteron beams (15.3 and 6.8 MeV, respectively) extracted from the PETtrace medical cyclotron at the Radiopharmaceuticals Production and Research Centre in the University of Warsaw, Heavy Ion Laboratory, 28 MeV protons from the C30 cyclotron at the National Centre for Nuclear Research, Swierk, near Warsaw and 33 MeV protons from the ARRONAX accelerator, Nantes were used to produce and investigate the medically interesting Sc radioisotopes. Both natural and isotopically enriched CaCO3 and TiO2 targets were used (42Ca, 43Ca, 44Ca, 48Ca, 48Ti). The production efficiency and isotopic purity were determined and are reported here for the highest commercially available enrichments of the target material. The Thick Target Yield, Activities at the End of Bombardment (EOB) and the relative activities of produced impurities at EOB are reported for 43Sc, 44gSc, 44mSc and 47Sc produced with particle energies below 33 MeV.

High Seroprevalence of CMV Among Women of Childbearing Age Implicates High Burden of Congenital Cytomegalovirus Infection in Poland.

Cytomegaloviruses are common worldwide, with variable frequency of infections. The infection in pregnancy may lead to pregnancy loss or serious sequelae for the child. To understand the risk posed by CMV in Poland we conducted cross-sectional study on women aged 15-49 basing on existing serum bank. Age dependent incidence, the rates of congenital infection and sequelae were modelled from sero-prevalence, literature and demographic data. The overall anti-CMV IgG prevalence was 81.9% increasing from 74.3% in <30 years old to 94.3% in subjects 45+ years old. The lowest incidence was estimated at the age of 15 and the highest at the age 34 (3.8 and 8.95 respectively/100 women/year). The estimated rate of cCMV varies from 22.4 to 37.2 per 1000 live birth depending on the assumptions made. The proportion of cases due to secondary infection ranged from 34.8% to 49.9% accordingly.

Production of medical Sc radioisotopes with an alpha particle beam.

The internal α-particle beam of the Warsaw Heavy Ion Cyclotron was used to produce research quantities of the medically interesting Sc radioisotopes from natural Ca and K and isotopically enriched 42Ca targets. The targets were made of metallic calcium, calcium carbonate and potassium chloride. New data on the production yields and impurities generated during the target irradiations are presented for the positron emitters 43Sc, 44gSc and 44mSc. The different paths for the production of the long lived 44mSc/44gSc in vivo generator, proposed by the ARRONAX team, using proton and deuteron beams as well as alpha-particle beams are discussed. Due to the larger angular momentum transfer in the formation of the compound nucleus in the case of the alpha particle induced reactions, the isomeric ratio of 44mSc/44gSc at a bombarding energy of 29MeV is five times larger than previously determined for a deuteron beam and twenty times larger than for proton induced reactions on enriched CaCO3 targets. Therefore, formation of this generator via the alpha-particle route seems a very attractive way to form these isotopes. The experimental data presented here are compared with theoretical predictions made using the EMPIRE evaporation code. Reasonable agreement is generally observed.

Cyclotron production of (43)Sc for PET imaging.

BACKGROUND: Recently, significant interest in (44)Sc as a tracer for positron emission tomography (PET) imaging has been observed. Unfortunately, the co-emission by (44)Sc of high-energy γ rays (E γ = 1157, 1499 keV) causes a dangerous increase of the radiation dose to the patients and clinical staff. However, it is possible to produce another radionuclide of scandium-(43)Sc-having properties similar to (44)Sc but is characterized by much lower energy of the concurrent gamma emissions. This work presents the production route of (43)Sc by α irradiation of natural calcium, its separation and purification processes, and the labeling of [DOTA,Tyr3] octreotate (DOTATATE) bioconjugate. METHODS: Natural CaCO3 and enriched [(40)Ca]CaCO3 were irradiated with alpha particles for 1 h in an energy range of 14.8-30 MeV at a beam current of 0.5 or 0.25 µA. In order to find the optimum method for the separation of (43)Sc from irradiated calcium targets, three processes previously developed for (44)Sc were tested. Radiolabeling experiments were performed with DOTATATE radiobioconjugate, and the stability of the obtained (43)Sc-DOTATATE was tested in human serum. RESULTS: Studies of (nat)CaCO3 target irradiation by alpha particles show that the optimum alpha particle energies are in the range of 24-27 MeV, giving 102 MBq/µA/h of (43)Sc radioactivity which creates the opportunity to produce several GBq of (43)Sc. The separation experiments performed indicate that, as with (44)Sc, due to the simplicity of the operations and because of the chemical purity of the (43)Sc obtained, the best separation process is when UTEVA resin is used. The DOTATATE conjugate was labeled by the obtained (43)Sc with a yield >98 % at elevated temperature. CONCLUSIONS: Tens of GBq activities of (43)Sc of high radionuclidic purity can be obtainable for clinical applications by irradiation of natural calcium with an alpha beam.

[Measles virus stimulation effect on the expression of Toll-like receptors in PBMC]. / Wplyw stymulacji wirusem odry na ekspresje receptorów Toll-like w komórkach PBMC.

INTRODUCTION: Toll-like receptors (TLRs) are an important component of a innate immune system. Stimulation of TLRs, through action with helper T cells, could change Th1/Th2 balance and thus affect adaptive immune response. Receptors TLR2 and TLR4 play important role in immune response to measles virus. The aim of this work was stimulation of the peripheral blood mononuclear cells (PBMC) and determination of Toll-like gene expression in these cells. METHODS: PBMCs from 20 healthy donors were stimulated with measles viruses and ligands for TLR2 and TLR4. For examinations the real time RT-PCR (QuantiFast® Assay, Qiagen) was used. The expression of Toll-like receptors was determined on muRNA level, using real-time one step RT-PCR (QuantiFast® Assay, Qiagen) with simultaneous detection of TLR2 and TLR4 genes and housekeeping gene (GAPDH). RESULTS: Virus-specific influence of wild measles virus strains activity on PBMC derived from vaccinated seronegative individuals manifested in higher level of expression of TLR2 and TLR4 genes in compare to the expression of these genes in PBMC of seropositive individuals. CONCLUSIONS: Toll-like receptors participate in the development of immune response to measles virus.

The significance for epidemiological studies anti-measles antibody detection examined by enzyme immunoassay (EIA) and plaque reduction neutralization test (PRNT).

The paper discusses the role of anti-measles antibodies for protection and significance for epidemiological studies determination of antibodies by different serological methods. The comparison of anti-measles virus antibodies levels measured by enzyme immunoassay (EIA) and Plaque Reduction Neutralization Test (PRNT) was described. It was found that the 200 mIU/ml of anti-measles activity measured by PRNT (level protection against symp- tomatic disease) is equivalent of 636 mIU/ml measured by EIA (Enzygnost®Anti-Measles Virus/IgG, Simens).

[The prevalence of active infection with viruses from the family Herpesviridae among members of families with children]. / Czestosc wystepowania aktywnych zakazen wirusami z rodziny Herpesviridae wsród czlonków rodzin wychowujacych dzieci.

INTRODUCTION: Cytomegalovirus infection (CMV) is one of the most common viral infections during pregnancy and one of the most common causes of birth defects in newborns. CMV infection occurs mostly through close contact with small children who can secrete the virus in saliva and urine. Children, especially in preschool and early school can also be a source of infection with other herpesviruses. The aim of the study was to determine the prevalence of active infections caused by viruses from the family Herpesviridae (CMV, EBV, VZV) among members of families with children. MATERIAL AND METHODS: The study included 24 families raising children aged from 2 to 18 years. From all members of the families (46 adults and 39 children) saliva samples were collected from which DNA was extracted. The isolated DNA samples were tested for the presence of CMV, EBV, VZV genetic material by nested PCR. In addition, each family carried out a survey. RESULTS AND CONCLUSIONS: The presence of CMV DNA in saliva samples were detected in members of 7 families and the presence of EBV DNA were detected in members of 11 families. Total DNA of CMV was detected in 8/85 samples of saliva (9.41%), of which 1/46 adults (2.17%) and 7/39 children (17.95%) and EBV DNA was detected in 18/85 tested saliva samples (21,18%) - 13/46 samples from adults (28,26%) and 5/39 samples from children (12,82%). VZV DNA was not detected in any of the tested saliva samples. The obtained results indicate that the active, asymptomatic infections with lymphotropic herpesviruses are common and affect more than 10% (CMV) and 20% (EBV) subjects.

Response of viral specific CD4 T cells to in vitro stimulation with vaccine and wild measles virus strains in vaccinated and naturally infected subjects.

With the implementation of the WHO strategic plan for the elimination of measles, the number of measles cases in European Region has decreased. However, outbreaks are still observed. Although most measles cases affect unvaccinated individuals, cases with vaccinated persons are also reported. Furthermore, it was described that a high percentage of young people in Poland exhibit no presence of anti-MeV IgG despite the high level of vaccination covering no less than 97% of the Polish population. Strong evidence exists that immunity to measles is complex and depends on both the humoral and cellular response and although antibodies have been used as correlates of immunity, it is increasingly being considered that antibody-based definitions of vaccine success or failure may be incomplete. Here, we investigated immunity to measles as the reactivity of CD4 T cells to stimulation with vaccine as well as wild strains of measles virus (MeV) isolated in Poland, in young vaccinated persons and subjects infected naturally. Evidence for the presence of MeV-specific memory cells years after infection or vaccination was found, however the cells ofvaccinees and naturally infected subjects reacted differently in contact with wild and vaccine MeV strains. Furthermore, the presence of a significant proportion of non-responder vaccinees was observed. In conclusion, our results may have implications for studies on the monitoring of the complexity of post-vaccine immune response.

[The use of real-time RT-PCR method for the determination of Toll-like genes expression at mRNA level]. / Zastosowanie metody real-time RT-PCR do oznaczania ekspresji genów receptorów Toll-like na poziomie mRNA.

INTRODUCTION: Toll-like receptors (TLRs) are an important component of a innate immune system. Stimulation of TLRs, through action with helper T cells, could change Th1/Th2 balance and thus affect adaptive immune response. The aim of this work was to optimize the stimulation of the peripheral blood mononuclear cells (PBMC) and the validation of real-time RT-PCR method for determination of Toll-like gene expression in these cells. METHODS: PBMCs from healthy donors were stimulated with measles viruses and ligands for TLR2 and TLR4. For examinations the real time RT-PCR (QuantiFast Assay, Qiagen) was used. Fold change of TLRs expression was normalized to GAPDH and estimated by 2(-deltadeltaCt) method. Validation of real-time RT-PCR method was performed for repeatability and efficiency. RESULTS: The level of gene expression varies between individuals and was dose and time of incubation dependent. The efficiency ofreal-time RT-PCR was 90.4% +/- 10.2 for GAPDH, 87.0% +/- 8.2 for TLR2 and 44.5% +/- 9.2 for TLR4. Repeatability, expressed as relative standard deviation (RSD) for Ct values was less than 0.70% for GAPDH, < 3.2% for TLR2 and < 2.84% for TLR4. CONCLUSIONS: Based on obtained results, the optimal conditions for stimulation were: 10 microg/ml/24h for LPS, 1 microg/ml/6h for Pam3CSK4 and 1250 MeV infectious particles/24h.

The influence of toll-like receptor stimulation on expression of EBV lytic genes.

Epstein-Barr virus (EBV) establishes latency in the resting memory B-cell compartment. It has been recently suggested that maintenance of chronic infection is dependent on periodic reactivation. Although the stimuli for EBV reactivation in vivo during natural infections are largely unknown, there is evidence indicating that heterologous infections could trigger herpesviruses reactivation. The purpose of this work was to identify the influence of Toll-like receptors stimulation on EBV replication in EBV latently infected Burkitt lymphoma cells (P3HR-1, Raji and Namalwa). The cells were stimulated with Pam3CSK4 (synthetic triacylated lipoprotein), PolyI:C (synthetic analog of dsRNA), LPS (lipopolysaccharide from E.coli), measles virus (MeV) and PMA (phorbol myristate acetate). Non-stimulated cells (NS) served as control. EBV expression was investigated at mRNA level for three viral lytic genes: BZLF1 (immediate early, ZEBRA), BALF2 (early, EA) and BcLF1 (late, VCA). Additionally, the effect of stimulation on NF-kBp65 and inflammatory cytokines (IL-lb, IL-6, IL-8, IL-10, IL-12p70, and TNF) was investigated. Stimulation of TLRs led to limited changes in EBV expression manifesting as increase of ZEBRA at mRNA level in cells treated with PolyI:C and Pam3CSK4. Stimulation with PolyI:C, Pam3CSK4 and LPS also lead to considerable increase of NF-kBp65, while increased levels of inflammatory cytokines were observed for IL-8, TNF and IL-6 in cells treated with PMA and MeV. In conclusion, the results of our experiments support the suggestion that TLRs stimulation with microbial ligands influences EBV virus replication.

[Influence of selected preanalytical factors on viral DNA detection by PCR method]. / Wplyw wybranych czynników przedanalitycznych na wyniki oznaczen wirusowego DNA metoda PCR.

INTRODUCTION: Obtaining a reliable laboratory test result depends on many factors, among which preanalytical factors play a significant role. The aim ofthis study was to determine the effect of temperature, storage time of samples and number of freezing and thawing cycles on the results of tests carried out by PCR. METHODS: The study was conducted in a model of cytomegalovirus (DNA) and with four types of clinical material: whole blood, serum, cerebrospinal fluid, urine and archival samples. After contamination with CMV clinical samples were incubated under various conditions for a specified period of time or subjected to cycles of freezing and thawing. The presence of DNA - CMV were determined by nested PCR method. RESULTS: The results revealed that in the case of applied levels of contamination and in model used in the study: 1) CMV DNA in samples of clinical material (blood, serum, cerebrospinal fluid, urine) for testing by PCR remains stable for at least 5 days at room temperature or refrigerated and at least 7 days when frozen, 2) Repeated freezing and thawing clinical specimens has no influence on the result of the presence of viral DNA, 3) Isolated viral DNA is stable in the temperature of the freezer and can be subjected to at least 20 freeze-thaw cycles without affecting the PCR results. CONCLUSIONS: Viral DNA in clinical specimens examined in the applied experimental conditions is stable.

[Presence of IgG class antibodies anti-measles virus in sera of subjects in different age]. / Wystepowanie przeciwcial klasy IgG dla wirusa odry w surowicach os6b w róznym wieku.

INTRODUCTION: The increase of measles incidence in Poland was recently observed. Furthermore, the analysis of routine serological tests performed in the department of virology, NIPH-NIH revealed, that nearly half of young people (20-30 years old) have no antibodies against measles virus. The paper presents results of IgG specific for measles virus prevalence in the sera of vaccinated and unvaccinated subjects, which aimed to make the selection of groups for immunological memory research. METHODS: Total of 100 persons were examined based on results of determination of the presence of IgG anti-MeV: 26 people born before and 74 born after 1972 year. From this group, 55 participants were selected for further study and divided into 3 groups (1) subjects born before 1972, unvaccinated against measles and seropositive as a result of natural infection, (2) subjects born after 1972, vaccinated against measles but seronegative or with traces ofanti-MeV IgG presence, (3) subjects born after 1972 seropositive due to vaccination. Selected persons are subject to further examinations include determination the number of leukocytes and lymphocytes profile. RESULTS: The level of anty-MeV IgG antibodies in subjects after natural infection was significantly higher compared to levels obtained by vaccinations. No significant differences in the immunological parameters which could influence on immune response were observed. CONCLUSIONS: Obtained results lead to search other factors that may affect the weak postvaccinal humoral response.

[Effect of stimulation with the measles virus on expression of early activation markers on CD4+ T lymphocytes]. / Wplyw stymulacji wirusem odry ekspresji wczesnych markerów aktywacji limfocytów T CD4+.

Elimination of measles is one of the priority plans of WHO. The success of this plan depends on the development of long lasting, postvaccinal immune response. The aim of this study was to present the effect of stimulation with different strains of measles virus on the expression of T-helper cell (CD4+ T) early activation markers in people with different history of measles infection and to determine the correlation between the activation and dose of virus used for stimulation. The study was conducted using material derived from two patients: one seropositive due to natural infection and one vaccinated, with traces of anti-MeV IgG antibodies. In the CD4 T helper cells, the expression of CD69 receptor and the ability of the cells to produce INF after stimulation with the vaccine-derived or wild-type strain of measles virus was determined. For antigen-specific stimulation the virus suspension containing about 100 infectious particle, its tenfold and hundredfold dilutions was used. We found that the expression of T-helper cells early activation markers depended on the strain of the measles virus used for the stimulation, type of the immune response (postvaccinal, natural infection), and in the case of CD69 expression also on the dose of the virus used for the stimulation.

Etiology of measles suspect cases reported in 2006-2007 in Poland.

To achieve measles elimination, an efficient surveillance system for rash illnesses is necessary. The aim of the present study was to ascertain which viruses, other than measles, are causing measles-like illnesses (MLIs) in Poland. Serum samples (n=278) collected from MLI cases and submitted to the National Reference Laboratory during 2006-2007 were investigated for anti-measles (MeV), rubella (RUBV), parvovirus B19 (B19V), Epstein-Barr (EBV) and herpesvirus type-6 (HHV-6) IgM presence. Age was strongly associated with MLIs etiology. In the youngest age group, 0-4 years, MeV and HHV-6 infection were prevailing, while in group of 5-9 years--RUBV and B 19V. Measles was confirmed more often in patients with high fever (p < 0.001) and with rash lasting longer than 5 days (p < 0.001). The type of rash was not significantly associated with MeV infection. Our results strongly suggest that according to WHO EURO strategic plan, Poland is close to elimination phase. High number of MLIs were caused by pathogens other than measles. Addition of anti-B 19V IgM testing to routine MLIs screening protocol may improve system performance in the more advanced stages of measles elimination.

[Toll-like receptors expression on Burkitt lymphoma cells]. / Ekspresja receptorów Toll-like na komórkach chloniaka Burkitta.

Toll like receptors (TLRs) are an important component of the immune response. They are link between innate and adaptative response. Lymphocytes B express most of the toll-like receptors and they may respond to a broad spectrum of PAMP. Lymphocytes B are one of the major lymphocyte populations in secondary lymphoid tissues, where they represent up to 50% of cells population. These cells are an important element of the defense, largely by using the mechanisms associated with innate response. On the other hand, lymphocytes B are the site of EBV latency, so Burkitt lymphoma cells can may be a convenient model to study the mechanisms associated with EBV infection. The aim of study was to determine the expression of TLRs at the m-RNA level of in Burkitt lymphoma cells treated with ligands for selected TLRs. P3HR, Raji and Namalwa cells were stimulated with Pam3 (10 microg/ml), PolyI:C (25 microg/ml), LPS (10 microg/ml) and measles virus (MeV, moi 0.02). Unstimulated cells and cells treated with PMA (0.5 microg/ml) served as negative and positive controls. After incubation, from stimulated and unstimulated cells mRNA was extracted, RT-PCR reaction was performed and electrophoretic separation was made. The intensity (INT) of bands were determined using the tools for quantitative analysis. In order to analyze the expression of TLR genes, INT values for TLR2, TLR3 and TLR4 in tested cell lines are expressed as %, assuming an average level of GAPDH expression as 100%. The 25% of INT for negative control was accepted as a change in expression level. It was found that the expression of Toll-like receptors in Burkitt lymphoma cells is diverse both in terms of cell type and the type of stimulation.

[Raji, P3HR-1 and Namalwa cells as a model for the study of Epstein-Barr virus (EBV) reactivation]. / Komórki Raji, P3HR-1 i Namalwa jako model badania reaktywacji zakaienia wirusem Epsteina-Barr (EBV).

The aim of the study was to characterize Raji, P3HR-1 and Namalwa cell lines in the aspect of their usefulness for the research on virus Epstein-Barr (EBV) reactivation, with the participation of Toll-like receptors (TLR). During a 12-day experiment, optimal conditions of cultivation (RPMI with 10% FCS at 37 degrees C in 5% CO2) were determined. In these conditions cells showed logarithmic growth. The presence of the DNA EBV was confirmed by the PCR method, showing that 12-day long maintenance of cells does not cause the loss of the virus. The presence of genes encoding TLR2, TLR3 and TLR4 was also confirmed by PCR. The TLRs expression at the mRNA level in cells subjected to 24h stimulation with TLR2, TLR3 and TLR4 agonist (Pam3CSK4, Poly(I:C) and LPS, respectively) was determined by the RT PCR method. The presence ofTLR4 mRNA was confirmed in the case of Namalwa cells stimulated by Pam3CSK and LPS, and P3HR cells stimulated by Pam3CSK4. In the case of Raji cells the expression of none of the receptors was confirmed at the mRNA level in cells with and without stimulation.

[Evaluating of influence of repeated thaw/freeze cycles on IgG and IgM stability]. / Wplyw wielokrotnego rozmraiania próbki na stabilnosc przeciwcial klasy IgG i IgM.

The purpose of this study was evaluating influence of repeated cycles of thawing and freezing serum samples on IgG and IgM stability. Serum positive samples for anti-cytomegalovirus and antimeasles virus IgG and/or IgM were aliquoted. Tubes containing 100 microl aliquot were frozen at -20 degrees C. Samples were repetitively thawed and froze in one to ten cycles. Antibodies presence was examined with commercially available ELISA tests. All samples reminded positive even after ten repeated thaw/freeze cycles.

[Immunity against tick borne encephalitis virus (TBE) in population of forest workers in Bialowieza]. / Odpornosc dla wirusa kleszczowego zapalenia mózgu (kzm) w populacji pracowników lesnych z terenu Bialowiezy.

In Poland, 200 cases of tick borne encephalitis are annually registered. It is about half of all registered cases of viral encephalitis. Immunity acquired after vaccination with TBE inactivated vaccine persists defined time dependent on number of dose of vaccine and individual features of vaccinated person. The aim of this paper was to determine the frequency of IgG antibodies against TBE virus among forestry workers from Bialowieza National Park with regard to information about vaccination against TBE virus. In the group of 59 persons vaccinated against TBE virus, 54 (91.5%) had IgG antibodies against TBE virus. In the group of 32 persons (non-vaccinated or for whom the information about vaccination was not given) 26 (81.3%) were seropositive. Relationships between VE value (determining level of antibodies), age and period passed from the last dose of vaccination were analysed. Taken to account the most disadvantageous circumstances (age = 60, regression intercept minus two standard deviation) antibodies level of VE = 11 (lower limit of positive result) remains for 2,72 years from last dose of vaccine against TBE virus. This result confirm recommendation about necessity to use of complementary dose within 3-5 years, at the same time it should be considered recommendation of necessity ofrevaccination persons 60 years old or above as frequently as every 3 years.