Tick-borne encephalitis: Burden of disease and impact of vaccination, Austria (2000-2024).

BACKGROUND

Tick-borne encephalitis (TBE) incidence has increased across Europe in the past decade, even in Austria which has the highest vaccination coverage in Europe. This study investigated the field effectiveness of TBE vaccination using nationwide hospital-based surveillance data (2000-2024), and examined age-specific differences in vaccine effectiveness and disease severity.

METHODS

We conducted a retrospective analysis of laboratory-confirmed TBE cases in Austria using nationwide hospital-based surveillance from 2000 to 2024. Annual TBE incidence rates were calculated for populations with regular, irregular, and no TBE vaccination. Vaccine effectiveness was estimated based on relative differences in incidence between vaccinated and non-vaccinated groups. Additionally, the number of cases prevented by vaccination from 2000 to 2024 was estimated, including TBE hospitalizations, severe cases, and deaths.

RESULTS

Among 2260 hospitalized TBE cases, 274 (12 %) occurred in children (1-15 years), 1066 (47 %) in adults (16-59 years), and 920 (41 %) in older adults (≥ 60 years). Severe disease was documented in 1051 (47 %) patients, and 26 (1.2 %) patients died. TBE vaccination provided excellent protection (99 % with regular and > 90 % with irregular vaccination schedules) and prevented more than 10,000 hospitalizations, 4000 severe cases, and 80 deaths between 2000 and 2024. Our data, however, revealed that vaccine uptake and schedule adherence declined over time, coinciding with increasing case numbers in unvaccinated and irregularly vaccinated populations, which resulted in a significant rise in TBE incidence (p < 0.0001).

CONCLUSIONS

TBE vaccination substantially reduced disease incidence across all age groups. Sustaining high vaccination coverage and compliance with vaccine recommendations is needed to prevent TBE and reduce healthcare burden.