Tick‐Borne Encephalitis Virus Surveillance—Vaccination‐ and Infection‐Induced Seroprevalences in Western Austria 2024

ABSTRACT

Reported tick‐borne‐encephalitis (TBE) cases have been increasing in Western Austria, but no data are available on vaccination‐ and infection‐specific seroprevalence. This study aimed to estimate current TBEV‐seroprevalence in the region and inform prevention programs by comparing anti‐NS1‐based‐incidence rates with reported case numbers and vaccination coverage. Between December 2023 and February 2024, serum samples from 4619 blood donors in Western Austria were collected and analyzed using TBEV‐ and WNV‐IgG‐ELISA assays. Seropositive samples were tested with a TBEV‐anti‐NS1‐IgG‐ELISA to distinguish infections from vaccinations. Borderline samples were retested with serum neutralization and triple‐NS1‐assays. The overall anti‐TBEV‐IgG‐seroprevalence was 80.1% (95%CI 78.9–81.3); 2.7% (95%CI 2.3–3.2) of donors tested positive for anti‐TBEV‐NS1 IgG antibodies, indicating previous infection. The notified incidence rate in Western Austria was 2.7/100 000/year, compared to 136.2/100 000/year based on anti‐TBEV‐NS1‐seropositive donors, denoting a substantial number of unreported cases (mean manifestation index 1.9%). The number of donors with TBEV‐infections varied considerably by district, highlighting potential hotspots for TBEV‐infections. The high anti‐NS1‐based, estimated annual TBE incidence rates show significant differences between districts, highlighting the need for targeted prevention programs. The high rate of undiagnosed TBE cases further suggests that estimated anti‐NS1‐based incidence rates should be considered when defining high‐risk areas.