What question did this study set out to answer?

The aim was to analyze TBEV sero-epidemiology and vaccination rates in Upper Austria.

March 4, 2026Open Access

Infection and Vaccination-Induced Tick-Borne Encephalitis Virus IgG Antibody Prevalence in the Austrian Federal State of Upper Austria, a High-Risk Region for TBEV

Key Points

The aim was to analyze TBEV sero-epidemiology and vaccination rates in Upper Austria.
Developed an anti-TBEV-NS1-IgG assay and neutralization test.
Screened blood donor samples from all districts in Upper Austria.
Differentiated between vaccine- and infection-induced antibodies.
Matched results with donor demographics such as age and gender.
2162 blood donor samples were analyzed.
87% of donors showed anti-TBEV-IgG from past vaccinations.
13.3% of unvaccinated males and 9.9% of unvaccinated females had signs of past TBEV infection.
Overall seroprevalence was 74/100,000; in non-vaccinated, it was 594/100,000.
The manifestation index for symptomatic cases was calculated at 2.8%.

Abstract

Background/Objectives: Tick-borne encephalitis (TBE) is the most important tick-borne viral central nervous system (CNS) infection in Europe and Asia. Since the introduction of a vaccine in Austria in the late 1970s, sero-epidemiological studies on the true incidence of tick-borne encephalitis virus (TBEV) infection in the population have been difficult, because it was not possible to distinguish between vaccine- and infection-induced antibodies. The goal of our study has been to analyze the sero-epidemiology of TBEV infections, vaccination protection rate, and manifestation index of the disease in the region of interest. Methods: Applying a newly developed anti-TBEV-NS1-IgG assay and the neutralization test, the protection and infection rates in blood donors of the Austrian Federal State of Upper Austria.It is one of the first areas in Austria, where the TBEV vaccine had been rolled out and broadly used. Samples from blood donors of all districts of the Federal State of Upper Austria were screened for anti-TBEV-IgG. Positive sera were differentiated for infection- and vaccine-induced antibodies. The results were matched with donor age, gender, and geographical origin. Results: 2162 samples were analyzed. A total of 87.0% of the blood donors tested showed anti-TBEV-IgG related to past TBEV vaccination. Within the unvaccinated group, a total of 13.3% of male and 9.9% of female blood donors exhibited anti-TBEV-NS1-IgG, indicating a past TBEV infection. The anti-TBE-NS1-IgG seroprevalence was determined at 74/100,000 for the whole population and at 594/100,000 in the non-vaccinated population. The manifestation index (MI) was calculated at 2.8%. The MI is defined as the probability or percentage of infected individuals who develop clinical symptoms of a disease. Conclusions: Our data provide evidence of a continuing high risk of TBEV infection in the Federal state of Upper Austria. The non-vaccinated population has an eightfold higher infection prevalence compared to the whole population. The MI of TBEV for severe infection seems lower as detailed in previous reports.

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