OBJECTIVES: Tick-borne encephalitis (TBE) is an infection by the tick-borne encephalitis virus (TBEV) that results in symptoms of central nervous system inflammation. TBE is endemic in Latvia and other European countries. TBE vaccines are commonly used in Latvia, but vaccine effectiveness estimates are limited.
METHODS: Study staff at Rīga Stradinš University conducted nationwide active surveillance for TBEV infections. Serum and cerebrospinal fluid were ELISA-tested for TBEV-specific IgG and IgM antibodies. Vaccination history was collected by interview and medical record review. Utilising data from surveillance and population surveys, vaccine effectiveness (with 95% confidence intervals) and cases averted were estimated using the screening method.
RESULTS: There were 587 laboratory-identified TBE cases from 2018-2020; 98.1% (576/587) were unvaccinated, 1.5% (9/587) were unknown or partially-vaccinated, and 0.3% (2/587) were fully-vaccinated (three-dose primary series and appropriately timed boosters). TBE resulted in the death of 1.7% (10/587) of TBE cases. TBE vaccine history was ascertained from 92.0% (13,247/14,399) people from the general population: 38.6% (5113/13,247) were unvaccinated, 26.3% (3484/13,247) were fully-vaccinated, and 35.1% (4650/13,247) were partially-vaccinated. TBE vaccine effectiveness was 99.5% (98.0-99.9) against TBE, 99.5% (97.9-99.9) against TBE hospitalisation, 99.3% (94.8-99.9) against moderate/severe TBE, and 99.2% (94.4-99.9) against TBE hospitalisation >12 days. From 2018-2020, vaccination averted 906 TBE cases, including 20 deaths.
CONCLUSIONS: TBE vaccine was highly effective in preventing TBE, moderate and severe disease, and prolonged hospitalisation. To prevent life-threatening TBE, TBE vaccine uptake and compliance should be increased in Latvia and other European regions where TBE is endemic.
Field of Science*
- 3.2 Clinical medicine
- 3.3 Health sciences
- 1.1. Scientific article indexed in Web of Science and/or Scopus database