Encephalitis: Viral - Vaccinations

Highlights	Risk Factors	Vaccinations
Introduction	Prognosis	Prevention
Causes	Diagnosis	Resources
Symptoms	Treatment	References

Vaccinations

Certain vaccinationscan help prevent the diseases that can lead to encephalitis.

Measles

Measles used to be a very common childhood disease. In about 1 out of 1,000 cases it can lead to encephalitis or death. The risk for these severe complications is highest in the very young and very old. Aggressive vaccination programs have reduced the incidence of measles in the US to fewer than 100 cases a year. In very rare cases, encephalopathy (brain damage) associated with the live-measles vaccine has occurred, but the risk is far lower than brain events from the disease itself.

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Vaccine for Varicella Virus (Chicken Pox and Shingles)

Herpes zoster, or shingles, is a reactivation of the varicella virus, whichauses chicken pox. A live-virus vaccine (Varivax) produces persistent immunity against chicken pox. Data show that the vaccine can prevent chicken pox or reduce the severity of the illness even if it is used within 3 days, and possibly up to 5 days, after exposure to the infection. The vaccine is protective in about 85% of cases, and even if a vaccinated person becomes infected, the disease is almost always mild. In spite of some concerns, studies are also finding that protection is long lasting. The vaccine is now recommended for all children between the ages of 18 months and adolescence who have not yet had chicken pox.

Vaccine against Flaviviruses (West Nile Virus, Japanese Encephalitis Virus, St. Louis Encephalitis)

Researchers are investigating a number of vaccines against the flavivirus family of arboviruses.

A vaccine (JE-VAX) is currently available for Japanese encephalitis. In travelers, it is only recommended for those visiting rural areas in high-risk Asian countries for more than 30 days. These countries include China, Korea, India and neighboring areas, and Southeast Asia. The disease may occur with lower frequency in Japan, Taiwan, Singapore, Hong Kong, and eastern Russia. A new type of single-dose vaccine (ChimeriVax-JE) is currently in Phase III trials.

Two types of vaccines, chimeric and DNA, are under investigation for West Nile virus, but it will be several years before these vaccines become commercially available. The chimeric type of vaccine combines the genes of several different viruses. Promising results for a Phase I trial of the ChimeriVax-West Nile vaccine, which combines West Nile and yellow fever viruses, were reported in 2005. Also in 2005, the U.S. National Institute of Allergy and Infectious Disease began a small clinical trial of a DNA plasmid WNV vaccine.