Immunization, Vaccines and Biologicals

Tick-borne encephalitis

Tick-borne encephalitis is an important cause of viral infections of the central nervous system in eastern, central and northern European countries, and in northern China, Mongolia, and the Russian Federation.

Approximately 10 000–12 000 clinical cases of tick-borne encephalitis are reported each year, but this figure is believed to be significantly lower than the actual total. Most infections with the virus result from tick bites acquired during outdoor activities in forested areas.

Immunization offers the most effective protection. Currently, there are four widely used vaccines of assured quality: FSME-Immun and Encepur, manufactured in Austria and Germany respectively, and based on European strains of the virus; and TBE-Moscow and EnceVir, manufactured in the Russian Federation and based on Far-Eastern strains. The four vaccines are considered to be safe and efficacious.

Vaccination against the disease requires a primary series of 3 doses. Little information is available on the duration of protection following completion of the primary 3-dose immunization series and on the need for, and optimal intervals between, possible booster doses.

Since 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 even district level. Therefore, establishing case reporting of the disease is essential before deciding on the most appropriate preventive measures to be taken. Similarly, health authorities’ decision-making on programmatic vaccination could be informed by an analysis of the cost–effectiveness.

In areas where the disease is highly endemic (i.e. where the average prevaccination incidence of clinical disease is ≥5 cases/100 000 population per year), implying that there is a high individual risk of infection, WHO recommends that vaccination be offered to all age groups, including children. Where the prevaccination incidence of the disease is moderate or low (that is, the annual average during a 5-year period is <5/100 000) or is limited to particular geographical locations or certain outdoor activities, immunization should target individuals in the most severely affected cohorts.

People travelling from nonendemic areas to endemic areas should be offered vaccination if their visits will include extensive outdoor activities.

WHO position papers

Last reviewed: 6 February 2014