Bühler et al.
Tick-borne encephalitis and West Nile virus antibody prevalence in Hamburg, a flavivirus non-risk/low-risk area. Journal of Medical Virology. 2025;97:e70701. doi:10.1002/jmv.70701
Most tick-borne encephalitis (TBE) virus infections in Germany (approximately 85%) occur in the southern federal states of Bavaria and Baden-Württemberg. Although the geographic distribution of TBE has expanded to northern regions over the past two decades, Hamburg remains the only German federal state without a reported locally acquired TBE virus infection. However, the true epidemiology of TBE in Germany is incompletely understood. Many TBE virus infections present with an influenza-like or asymptomatic course and may therefore remain undiagnosed and unreported. Due to Hamburg’s non-risk status by the Robert Koch Institute and doctors’ lack of awareness of TBE in this federal state, this underreporting is evident.
To address this gap, a cross-sectional study was conducted to assess TBE antibody prevalence and vaccination-induced protection in Hamburg. A total of 1,321 blood donations from adult individuals collected in May 2023 were analyzed for antibodies indicative of prior TBE virus infection (anti-NS1) or vaccination (anti-glycoprotein E).
Four samples tested positive for anti-NS1 antibodies, indicating previous TBE virus infection. The resulting TBE seroprevalence was approximately tenfold lower than that observed in TBE risk areas in southern Germany. These infections were likely non-autochthonous and may have been acquired during stays in known TBE risk regions.
Approximately one quarter of blood donations tested positive for anti-glycoprotein E antibodies, consistent with previous TBE vaccination. In line with data published by the Robert Koch Institute, vaccination coverage in non-risk areas such as Hamburg is lower than in established risk areas, predominantly located in southern Germany. Given the increasing number of reported TBE cases in northern Germany, continued disease surveillance and preventive measures, including vaccination, are warranted.