Page 416 - TBE_Book_V2_2019

Chapter 12b: TBE in Sweden

As in other areas of Europe, the number of respondents reported being vaccinated
reported TBE cases has increased during the against TBE at least once. Based on these
last 25 years. The mortality of TBE in Sweden findings, the estimated TBE incidence in the
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is significant (1.4%) and the morbidity and unvaccinated regional population was 8.5–
long-term sequelae make it a disease of great 12/100,000, which is comparable to highly
importance in the endemic regions. 8–10 TBE endemic areas in the Baltics and Central
has been reported in Sweden from diagnostic Europe.
laboratories on a voluntary basis since the
1970s and notification is mandatory since The protection rate of the vaccine has been
2004. During the years 2007–2018, between estimated to be 96% to 98% according to field
181 and 391 (year 2017) cases of TBE were studies in Austria. In a study from 2010, data
reported annually in Sweden despite the fact from 27 Swedish patients with clinical
that vaccination has been increased in the symptoms and signs of TBE, together with
exposed population. There are 2 TBE vaccines serological evidence of TBEV infection despite
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available in Sweden: FSME-immun (Pfizer) active vaccination, was presented. These
introduced in 1988 and Encepur (Novartis vaccination failures were characterized by a
Vaccines) introduced in 2003. slow and initially non-detectable development
of TBEV-specific IgM, seen together with a
Vaccination against TBE is voluntary in rapid rise of IgG and neutralizing antibodies in
Sweden. The vaccination schedule recom- serum. The majority (70%) of the 27 patients
mended in Sweden follows the recommenda- were above age 50, which indicated the need
tions of the manufacturers, with one for a modified immunization strategy in the
exception being that after dose 4 and elderly (as noted above). Recently, a new tool
onwards, a 5-year interval is recommended, (TBE suspension multiplex immunoassay, TBEV
irrespective of age (the manufacturers recom- SMIA) for improved diagnostics of TBEV
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mend 3-year booster intervals after the age of infections was reported. The TBEV SMIA can
50). The change to a 5-year interval after dose accurately differentiate TBEV infections from
4 and onwards was based on a large study of vaccinations and further studies have now
the serological response in 535 persons in been initiated to evaluate the efficiency of the
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Sweden after TBE vaccination. However, if assay for diagnosis of potential vaccine
TBE vaccination is initiated over age 60, the failures.
recommended schedule is 1 extra dose 2
months after the second dose, i.e. the initial In northern Europe, including Sweden, TBEV-
vaccination includes 4 doses at 0, 1, 3, and 5- EU is usually transmitted to humans by the
12 months. common tick, Ixodes ricinus. Pettersson and
colleagues investigated the prevalence in host
The number of vaccine doses sold in Sweden -seeking I. ricinus in southern and central
has averaged from 500,000 to 600,000 Sweden and reviewed all relevant published
annually since 2006, but because TBE records on the prevalence of TBEV in ticks in
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vaccination is not included in any official northern Europe. The estimated mean
vaccination registry, the actual number of minimum infection rate (MIR) of TBEV in
immunized individuals is unknown. nymphal and adult I. ricinus for northern
Europe (i.e. Denmark, Norway, Sweden, and
To estimate the TBE vaccination coverage in Finland) was 0.28% and 0.23% for southern
the greater Stockholm region, a questionnaire Sweden. Also, the infection prevalence of
was sent to a randomized sample of 8,000 TBEV was significantly lower for nymphs
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individuals in 2013. Fifty-three percent of all (0.10%) than in adult ticks (0.55%). At a well-

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