TBE in Switzerland and Liechtenstein

Kyra Zens

E-CDC risk status: endemic

(last edited: date 29.04.2024, data from 2023)

History and current situation

Tickborne Encephalitis (TBE) was first reported in Switzerland in 1969.1 From the 1970s through the 1990s the causative agent, the tickborne encephalitis virus (TBEV), was found to be endemic in geographically localized areas within the northeastern part of the country.2-4 A formal case definition and surveillance activities were introduced in 1984 and TBE was made a mandatory notifiable disease in 1988.5 Currently, all suspected TBE cases are reported to the Swiss Federal Office of Public Health (FOPH) using a two-tiered system. First, all laboratory tests indicative of acute TBEV infection are reported to the FOPH. Then, attending physicians are requested to complete a notification form providing specific clinical information, which is forwarded to the cantonal physician for review and then returned to the FOPH (Table 1). Both laboratory and completed clinical reporting forms are registered and maintained by the FOPH.5 The TBE case definition used in Switzerland is based on a combination of clinical and laboratory criteria and is similar to, but differs slightly from, that used by the ECDC in that “possible” cases, in addition to “probable” and “confirmed” cases, are included (Table 1).6-9

The majority of TBE cases in Switzerland are reported between April and October (Figure 1).10 Cases are more commonly reported in men, compared to women, and individuals aged 50-69 are most affected, though a bimodal trend with a smaller peak in cases among children aged 5-9 is also observed (Figure 2).10 Recent work has demonstrated that approximately 5% of unvaccinated individuals throughout the country are seropositive, suggesting that exposures far outnumber clinically confirmed cases of disease.11 Among clinical TBE cases, approximately 75% recalled a tick bite within the 4 weeks prior to disease onset.6,8 Approximately 75% result in hospitalization. Meningitis is observed in 19-49% of cases,6,12,13 meningoencephalitis in 43-59% of cases,6,12,13 and meningoencephalomyelitis and/or radiculitis in 5-7%.6,12,13 Just under 1% of cases are fatal (Table 1).6,8,13

Over the last two decades, both the geographic range and total incidence of TBE cases have increased dramatically throughout Switzerland.10,14,15 From an initial localization to the northeastern part of the country, TBE cases have increasingly been reported further west- and southward. This has been paralleled by increases in the range of TBEV-infected ticks16-23 and small and large mammal populations with positive anti-TBEV serology (Table 1).24-28 Currently, TBEV has been identified in ticks from most regions of Switzerland and in Liechtenstein, and, accordingly, human cases are now found in most areas of the country.29 In 2020, the nationwide average disease incidence exceeded the WHO’s definition of “highly endemic”, with greater than 5.0 cases/100,000 individuals reported.10

Official recommendations for vaccination against TBE have been in place in Switzerland and Liechtenstein since 2006; initially for all individuals aged 6 and older living or spending significant time in 71 “high risk” areas throughout both countries (Table 1).30 These risk areas, based on reported cases and viral surveillance in the environment, were updated and expanded annually to reflect the changing epidemiology of the disease.29,31 The resulting risk area map (Figure 3) was used until 2018 to define TBE vaccination recommendations throughout the country.29,31 However, in 2019, in view of the continuing increases in incidence and geographic range of disease, health authorities in Switzerland and Liechtenstein expanded the risk area and simplified the vaccination recommendation to cover the entirety of both countries – with the exceptions of the Swiss cantons of Geneva and Ticino14,29 (Figure 3a – 3c). In 2024 the recommendation was further revised to include the canton of Geneva (from summer 2024) as well as to recommend vaccination beginning at 3 years of age.32

Vaccination is reimbursed by compulsory health insurance for individuals to which the recommendation applies; namely those 3 years of age and older living or spending significant time in risk area.14,32 In children 1–2 years of age, vaccination is considered and reimbursed on a case-by-case basis.14,32 Considerations are also made for those with “high risk” occupations, though the cost of vaccination is to be reimbursed by the employer (Table 1).14,32 Nationwide, between 2020 and 2022, just 2% of 2-year-olds were vaccinated, increasing to 50% coverage among 8- and 16-year-olds. Among adults, from the most recent data in 2018, 42% had received at least one TBE vaccine dose while 33% had completed at least the three dose primary series (Table 1).33 Following completion of primary immunization, Switzerland has a unique recommendation for administration of booster vaccine doses every 10 years,30,34 unlike most other European countries and in contrast to the label. However, recent epidemiologic studies in the country have demonstrated that vaccine effectiveness (VE) remains high in both children35 and adults36 over this interval, with sustained protection for at least 10 years after the last vaccine dose was received.

Overview of TBE in Switzerland

Table 1: TBE in Switzerland
Viral subtypes, distributionOnly the European subtype has been described17,20,22,23
Reservoir animalsSmall mammals, generally rodents (Apodemus flavicollis, A. sylvaticus, Myodes glareolus), are the primary reservoir hosts for TBEV observed in Switzerland24
TBEV-infected ticks have also been found on migrating birds21
Infected tick species (%)Only Ixodes ricinus ticks described; Prevalence in ticks is focal and ranges widely, generally less than 1% of questing ticks but as high as 14.3%16-23,25,26,37
Dairy product transmissionNot documented, risk estimated to be low38
Case definition used by authoritiesPossible Case: positive IgM serology with influenza-like illness (ILI) or non-specific neurological signs & symptoms, OR, positive IgM + positive IgG serology without specific clinical symptoms
Probable Case: positive IgM serology with meningitis, meningoencephalitis, encephalomyelitis or radiculitis, OR, positive IgM + positive IgG serology with influenza-like illness (ILI) or non-specific neurological signs & symptoms
Confirmed Case: positive IgM + positive IgG serology with meningitis, meningoencephalitis, encephalomyelitis or radiculitis, OR, TBE-RNA detection by PCR with meningitis, meningoencephalitis, encephalomyelitis or radiculitis
Completeness of case detection and reportingCase reporting assumed to be complete or near complete due to two-tiered system5-8, though no specific studies have evaluated this
Type of reportingA mandatory notifiable disease since 1988 with reporting to the Swiss FOPH following a two-tiered system:5-8
-First, all laboratory tests positive for evidence of acute TBE are reported
-Afterwards, attending physicians are requested to complete a specific notification form providing specific clinical information
Other TBE-surveillanceNot routine
Studies assessing TBEV in ticks16-23,25,26,37
Studies assessing seropositive blood donors11
Special clinical featuresIn children:35
-No neurologic involvement reported in 13% of cases
-Meningeal irritation, meningitis observed in 35% of cases
-Meningoencephalitis in 49% of cases
-Encephalitis, encephalomyelitis, radiculitis, paresis reported in 3% of cases
 
In adults:
-Hospitalization observed in 71-75% of reported cases6,8,13
-Meningitis in 19-49% of cases6,12,13
-Meningoencephalitis in 43-59% of cases6,12,13
-Meningoencephalomyelitis/Radiculitis in 5-7% of cases6,12,13
-Slightly under 1% of cases are fatal6,8,13
Licensed vaccinesEncepur N® (Bavarian Nordic) Adult Formulation39
Encepur N® Kinder (Bavarian Nordic) Pediatric Formulation39
FSME-Immun® (Pfizer) Adult Formulation40
FSME-Immune® Junior (Pfizer) Pediatric Formulation41
Vaccination recommendationsLocalized recommendations based primarily on area of residence since 200630; in 2019 and 2024 the recommendation was expanded to cover all of Switzerland and Liechtenstein with the exceptions of Geneva and Ticino14,29,32
 
Vaccination is reimbursed by compulsory health insurance for individuals covered by the recommendation:
-Individuals 3 years of age and older living or spending significant time in risk areas14,32,33
-In children 1–2 years of age vaccination is considered and reimbursed on a case-by-case basis14,32,33
-For individuals with “high risk” occupations, costs of vaccination are covered by the employer14,32,33
Vaccine uptakeIn children34,43 – Average national vaccination uptake (3+ doses) 2019-2022:
-2 years old: 2.3% (1.8-2.9)
-8 years old: 48.7% (46.9-50.6)
-16 years old: 50.1% (48.3-52.0)
 
In adults35 – Average national vaccination uptake (3+ doses) 2018:
-18-39 years old: 34.7% (31.5–38.0%)
-40-59 years old: 31.3% (29.0–33.8%)
-60-79 years old: 32.4% (30.1–34.8%)
National Reference center for TBENationales Referenzzentrum für durch Zecken übertragene Krankheiten (NRZK; National Reference Centre for Tick-borne Diseases)
Website: www.swissticks.ch
 
The reference center consists of two partners:
Institut für Mikrobiologie des Centre Hospitalier Universitaire Vaudois (CHUV)
Rue du Bugnon 48
1011 Lausanne
Tél. +41 21 314 46 48 / +41 21 314 40 56 (secrétariat)
Tél. +41 21 314 49 79 (Prof. G. Greub)
Mail: gilbert.greub@chuv.ch
 
ADMED Microbiologie
Boucle de Cydalise 16+2300 La Chaux-de-Fonds
Tél. +41 32 967 21 01
Mail: admed.microbiologie@ne.ch

Figure 2: Age and gender distribution of TBE cases in Switzerland 2000–2023

Source data
Age Group (Years)Cases (Male)Cases (Female)(Unknown)
0-102121080
11-202331282
21-302221530
31-403532480
41-504663042
51-605013131
61-704702441
71-803401130
81+88380
Unknown100

Data includes all possible, probable, and confirmed cases according to Swiss TBE case definitions


Figure 3a: TBE cases – reported exposure sites, 2012-2023

Latest update available at: https://s.geo.admin.ch/727304e0f5


Figure 3b: Risk areas in Switzerland where TBE vaccination was recommended until the end of 2018


Figure 3c: Extended risk areas where TBE vaccination was recommended, 2019-2023. Risk areas were further extended for all individuals (residents and visitors aged 3+ years) with the exception of canton Ticino, from April 2024

Official update of map not yet available by April 30, 2024 but can be found afterward with latest update at: https://s.geo.admin.ch/727304e0f5

Acknowledgments

Unpublished data were kindly provided by Annora Mack and Ekkehardt Altpeter, Federal Office of Public Health FOPH, Division of Communicable Diseases, Bern, Switzerland.

Author

Kyra Zens

Contact

Kyra Zens
zens@immunology.uzh.ch

Citation

Zens K. TBE in Switzerland and Liechtenstein. Chapter 13. In: Dobler G, Erber W, Bröker M, Chitimia-Dobler L, Schmitt HJ, eds. The TBE Book. 7th ed. Singapore: Global Health Press; 2024. doi:10.33442/26613980_13-33-7

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