Peer-reviewed article
Tick-borne encephalitis in the Åland Islands, Finland: incidence and disease course since the implementation of a general TBE vaccination programme.
Jessica Tikkala, Christian Jansson, Gunilla Häggblom, Malin Ringbom, Mathias Grunér et al. ·
Summary
Written by AI, not yet AICS's view · claude-haiku-4-5-20251001This study examined tick-borne encephalitis (TBE) cases in Åland, Finland from 2006 to 2023 following the introduction of a vaccination programme. Among 145 patients diagnosed with TBE, about half were unvaccinated, one-third incompletely vaccinated, and 14% fully vaccinated. The vaccination programme appeared to prevent an increase in TBE incidence in the region compared to neighbouring areas, though the study found breakthrough infections occurred in vaccinated individuals. Most patients recovered within two years, but about 81% required hospitalization and the disease was more severe in older individuals.
Key points
- 145 TBE cases diagnosed over 18 years; 10% were children under 18 years old
- 50% of patients were unvaccinated, 32% incompletely vaccinated, 14% completely vaccinated
- TBE incidence remained stable at 29/100,000/year in Åland, unlike neighbouring regions which experienced increases
- 81% of patients were hospitalized; 9% required intensive care; 2 fatalities occurred
- 86% of patients were clinically recovered at two-year follow-up
Limitations
This is a retrospective study in a single endemic region with a small pediatric sample (10% of cases), so findings may not generalize to other populations or regions. The study cannot establish causality between the vaccination programme and the stable incidence without a comparison group that did not implement vaccination.
Abstract
Tick-borne encephalitis (TBE) is a potentially life-threatening viral disease with rising incidence in Europe. This retrospective study investigates the incidence, clinical course, and long-term outcome of TBE in Åland, a region endemic for the disease, following the introduction of a TBE vaccination programme in 2006. All patients diagnosed with TBE in Åland between 2006 and 2023, in accordance with the diagnostic criteria established by the European Centre for Disease Prevention and Control (ECDC), were included in the study. A review of medical records was conducted, and epidemiological and laboratory data were systematically collected. Disease severity and clinical outcome were assessed. TBE was diagnosed in 145 patients (66% male; median age 53 years; 10% children <18 years). The median TBE incidence was 29/100,000/year. Primary care was the first point of contact in 48% of cases. Of all patients, 72 (50%) were unvaccinated, 46 (32%) incompletely vaccinated and 20 (14%) completely vaccinated. Fifty-seven (39%) were diagnosed with meningitis and 88 (61%) with meningoencephalitis. Overall, 117/145 (81%) patients were hospitalized and 13/145 (9%) required intensive care. Severity of disease correlated with increasing age. Two fatalities occurred. Unlike neighbouring regions, Åland did not experience an increase in TBE incidence, likely due to the implementation of the vaccination programme. Most disease courses were monophasic and occurred in unvaccinated individuals. Surprisingly, a significant number of breakthrough infections were observed, particularly among those with incomplete vaccination, who more frequently developed severe disease. However, at two-year follow-up, 86% of patients were considered clinically recovered.