Seeking a Safer Vaccine against Japanese Encephalitis

Tuesday at the 2010 World Vaccine Congress in Lyon, France, Jason Golan, Product Manager for Intercell, spoke about the development process of his company’s vaccine for Japanese encephalitis (JE), one of the most common forms of viral encephalitis in Asia, with 30,000—50,000 cases reported annually. The JE virus is a mosquito-borne flavivirus and is endemic or epidemic in many tropical and subtropical countries in Asia. Golan said that the majority of infections in humans are asymptomatic but, when symptomatic, JE disease typically appears as a sudden onset of fever, complicated by neurological signs and symptoms due to neuroinvasion of the JE virus, and culminating in progressive coma. In symptomatic individuals who develop JE, 20–30% are likely to die and approximately 50% of the survivors are left with permanent neuropsychiatric sequelae. JE is a significant public health problem to persons who reside in endemic countries. Although the overall incidence rate of JE in travelers is low, the risk can be substantially increased by prolonged visits to rural areas and stagnant waters. Golan said there is no drug treatment for JE, only supportive care to ameliorate symptoms. Therefore, preventive vaccination remains an important control measure worldwide, and the CDC’s advisory committee for immunization practices (ACIP) recommends JE vaccination for travelers who plan to spend a month or longer in endemic areas. The CDC also suggests vaccination for short-term visitors under certain circumstances (eg, visits to rural areas).

A vaccine against Japanese Encephalitis has been available for travelers from the US (and Europe, on a named-patient basis); however, Golan said that its use has been limited due to concerns over its safety profile and a recent announcement of discontinued production. Searching for a safer alternative, Walter Reed Army Institute initiated development of a next-generation JE vaccine in the 1990s. After completing phase I and phase II trials, the vaccine was in-licensed by Intercell AG, which continued its product development through phase III clinical trials, industrialization, and licensure.

Today, the vaccine (known as Ixiaro) is licensed in the US, Europe, Canada, Switzerland, and Australia (as “Jespect”), providing a well-tolerated, effective, and convenient vaccine against JE, suitable for administration to travelers and military personnel who wish to reduce their risk of acquiring the disease.

Golan said that Ixiaro is indicated for active immunization against JE virus for persons 18 years and older (17 years of age and older in the US). It is a purified, inactivated, state-of-the-art JE vaccine that uses cell culture technology, provides a good immune response, and is well tolerated. It does not contain thimerosal, gelatin or any other stabilizers or preservatives in its formulation. The vaccine is provided as a ready-to-use liquid formulation in pre-filled syringes and is administered in two doses, 28 days apart.