Traveller vaccination tick-borne encephalitis

Template:Traveller vaccination human papillomavirus Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1];Associate Editor(s)-in-Chief: Seyedmahdi Pahlavani, M.D. [2]

Disease cause

• Tick-borne encephalitis virus.
• Three subtypes of the causative agent are known:

• • The European (Western)

• • The Far Eastern (spring-and-summer encephalitis) and
  • The Siberian.

Transmission

Tick-borne encephalitis virus is transmitted by the bite of infected ticks (which often remain firmly attached to the skin for days) or occasionally by ingestion of unpasteurized milk. There is no direct person-to-person transmission.

Nature of the disease

Infection may induce an influenza-like illness followed, in about 30% of cases, by high fever and signs of central nervous involvement. Encephalitis developing during this second phase may result in paralysis, permanent sequelae or death. Severity of illness increases with age of the patient.

Geographical distribution

Tick-borne encephalitis tends to occur focally even within endemic areas. Currently, the highest incidences of clinical cases are being reported from foci in the Baltic States, the Russian Federation and Slovenia. High incidences are also reported from foci in the NorthWestern Federal Area of the Russian Federation. Other countries that have reported cases within their territories, or that are considered to be at risk because of focally high prevalence of the virus in ticks, include Albania, Austria, Belarus, Bosnia, Bulgaria, China, Croatia, Denmark, Finland, Germany, Greece, Hungary, Italy, Mongolia, Norway, Poland, Republic of Korea, Romania, Serbia, Slovakia, Slovenia, Sweden, Switzerland, Turkey and Ukraine.

Risk for travellers

Travellers to endemic areas may be at risk during April to November. The risk is highest for people who hike or camp in forested areas up to an altitude of about 1500 m.

Precautions

Prevent blood-feeding ticks from becoming attached to the skin by wearing appropriate clothing, including long trousers and closed footwear, when hiking or camping in countries or areas at risk. Repellents containing diethyltoluamide provide relative protection for several hours. The whole body should be inspected daily and attached ticks removed as soon as possible. The consumption of unpasteurized dairy products should also be avoided in those areas.

Vaccine

The vaccine should be offered to people travelling from nonendemic areas to endemic areas if their visits will include extensive outdoor activities. The two vaccines manufactured in western Europe are considered to be safe and efficacious for individuals aged ≥1 year. Both vaccines are available in both adult and paediatric formulations. The two vaccines manufactured in the Russian Federation are also considered safe and efficacious for individuals aged ≥3 years although supporting data are more limited for the Russian products. In addition, one vaccine is manufactured and commercialized in China. Current vaccines appear to protect against all tick-borne encephalitis virus subtypes circulating in endemic areas of Asia and Europe. Vaccination against the disease requires a primary series of three doses; those who will continue to be at risk should probably have one or more booster doses. Little information is available on the duration of protection following completion of the primary three-dose immunization series and on the need for, and optimal intervals between, possible booster doses. Outside countries or areas at risk, tick-borne encephalitis vaccines may not be licensed and will have to be obtained by special request. As the incidence of tick-borne encephalitis may vary considerably between and even within geographical regions, public immunization strategies should be based on risk assessments conducted at country, regional or district level, and they should be appropriate to the local endemic situation.

Adverse reactions

With the western European vaccines, adverse events are commonly reported, including transient redness and pain at the site of injection in ≤45% of cases and fever ≥38 °C in ≤5% to 6%. However, none of these events is life-threatening or serious. Both the Russian vaccines have been reported to be moderately reactogenic. No information is available on the Chinese product.