A combined cross-sectional analysis and case-control study evaluating tick-borne encephalitis vaccination coverage, disease and vaccine effectiveness in children and adolescents, Switzerland, 2005 to 2022.

BackgroundTick-borne encephalitis (TBE) is a severe, vaccine-preventable viral infection of the central nervous system. Symptoms are generally milder in children and adolescents than in adults, though severe disease does occur. A better understanding of the disease burden and duration of vaccine-mediated protection is important for vaccination recommendations.AimTo estimate TBE vaccination coverage, disease severity and vaccine effectiveness (VE) among individuals aged 0-17 years in Switzerland.MethodsVaccination coverage between 2005 and 2022 was estimated using the Swiss National Vaccination Coverage Survey (SNVCS), a nationwide, repeated cross-sectional study assessing vaccine uptake. Incidence and severity of TBE between 2005 and 2022 were determined using data from the Swiss disease surveillance system and VE was calculated using a case-control analysis, matching TBE cases with SNVCS controls.ResultsOver the study period, vaccination coverage increased substantially, from 4.8% (95% confidence interval (CI): 4.1-5.5%) to 50.1% (95% CI: 48.3-52.0%). Reported clinical symptoms in TBE cases were similar irrespective of age. Neurological involvement was less likely in incompletely (1-2 doses) and completely (≥ 3 doses) vaccinated cases compared with unvaccinated ones. For incomplete vaccination, VE was 66.2% (95% CI: 42.3-80.2), whereas VE for complete vaccination was 90.8% (95% CI: 87.7-96.4). Vaccine effectiveness remained high, 83.9% (95% CI: 69.0-91.7) up to 10 years since last vaccination.ConclusionsEven children younger than 5 years can experience severe TBE. Incomplete and complete vaccination protect against neurological manifestations of the disease. Complete vaccination offers durable protection up to 10 years against TBE.