Vaccines for preventing tick-borne encephalitis

Tick-borne encephalitis (TBE) is a disease of the central nervous system caused by a tick-borne viral infection. TBE can lead to severe neurological syndromes, which can result in death. Many species of wild and domestic animals act as hosts of ticks; transmission to humans occurs often in woodland areas, especially during the summer, which is the time of greatest human outdoor activity. TBE is particularly prevalent in Central and Eastern Europe.

Although personal protective measures to avoid tick bites (such as insect repellents, avoidance of tick-infested areas, and use of protective clothing) are recommended, there is no effective treatment for TBE, and vaccination is the only preventive measure currently available.

This review evaluates the effectiveness and adverse events induced by current vaccines for preventing TBE. The authors identified 11 trials involving 8184 participants, which assessed different versions of three types of tick-borne encephalitis vaccines. No trials reported on cases of clinical TBE, but all tested vaccines were highly immunogenic. Adverse effects were commonly reported, none were serious or life threatening.

The authors recommend further trials or well-conducted observational studies with clinical outcomes (ie TBE cases) to better estimate vaccine effectiveness and the duration of vaccine protection, as well as long-term adverse events.

Authors' conclusions: 

Tick-borne encephalitis vaccines appear to be highly immunogenic, but the relationship between seroconversion and clinical protection has not been established. Although adverse effects were commonly reported, none were serious or life threatening.

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Background: 

Tick-borne encephalitis (TBE) is a disease of the central nervous system caused by a tick-borne viral infection. TBE can lead to severe neurological syndromes such as meningitis, meningoencephalitis, and meningoencephalomyelitis, which can result in death. There is no treatment, and prevention with the vaccine is the only intervention currently available.

Objectives: 

To evaluate vaccines for preventing TBE in terms of effectiveness and adverse effects.

Search strategy: 

In June 2008, we searched the Cochrane Infectious Diseases Group Specialized Register, CENTRAL (The Cochrane Library 2008, Issue 2), MEDLINE, EMBASE, LILACS, and mRCT. We also checked reference lists of articles.

Selection criteria: 

Randomized and quasi-randomized controlled trials comparing TBE vaccines against placebo, control vaccines, no intervention, or a different dose or schedule of the intervention vaccine.

Data collection and analysis: 

Two authors applied the inclusion criteria, extracted data, and assessed each trial's risk of bias. We could not combine the included trials in a meta-analysis because of differences in comparisons and outcomes.

Main results: 

Eleven trials (corresponding to 10 papers) involving 8184 participants (6586 adults and 1598 children) were included. Different versions of three types of TBE vaccines were tested (IPVE, FSME-IMMUN, and Encepur); out of which only three (Encepur children, Encepur Adults, and FSME-IMMUN "new") are currently licensed. No trials reported on cases of clinical TBE, but all reported on antibody titre (seroconversion). All the vaccines gave seroconversion rates of over 87%. Systemic and local adverse effects were common; none were severe or life threatening.

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