Tick-borne encephalitis (TBE) is an acute viral illness caused by two closely related memberss of the family Flaviviridae. The endemic area for tick-borne encephalitis (TBE) spreads from Alsace-Lorraine in the west to Vladivostok and north-eastern regions of China in the east, and from Scandanavia to Italy, Greece and Crimea in the south. TBE also is endemic in North Japan, where the virus has repeatedly been isolated from blood samples of sentinel dogs, ticks, and rodent spleens.
TBE is a serious acute central nervous system infection which may result in death or long-term neurological sequelae in 35–58% of patients. The proportion of cases involving subclinical infection varies between 70% and 98%. Symptomatic infection occurs in all age groups. In Asia, the disease is characterized by abrupt onset of fever, severe headache, nausea, vomiting and severe back pain often associated with focal epilepsy and flaccid paralysis, especially of the shoulder girdle. Such paralysis may be permanent. The central European form of the disease has a longer course, often with biphasic fever, but severe effects are less frequent. The initial febrile stage is normally not associated with infection of the central nervous system, but the second phase, following approximately 4-10 days after apparent recovery, is characterized by fever and meningoencephalitis. The case-fatality rate is approximately 20% for the Asian form of the disease and 1-5% for the European form.
Tick-borne encephalitis vaccines
The envelope glycoprotein of the TBE virus induces neutralizing and haemagglutination-inhibition antibodies and is the most important antigen for providing protection from disease. The first vaccine against TBE was prepared in 1941 in the brains of mice. Some 20 years later TBE vaccines derived from chicken embryo fibroblast cells were developed and used in humans in the former Soviet Union. Later, a purified, inactivated virus vaccine was developed which proved to be more immunogenic than previous TBE vaccines. The efficacy of these vaccines has been well documented. In addition, it has been demonstrated that antibodies induced by vaccination of human volunteers neutralized all tested virus isolates.
TBE Vaccine Standardization
WHO Recommendations for inactivated TBE vaccine were adopted by the Expert Committee on Biological Standardization in 1997 based on expert advice taking into consideration the regulations and quality requirements for the manufacture and control of TBE vaccines that have already been established in several countries.
Tick-borne encephalitis vaccine, inactivated, Requirements for tick-borne encephalitis vaccine (inactivated); Adopted 1997, TRS No 889, Annex 2
No WHO reference materials for tick-borne encephalitis vaccine are currently available.