Some Travelers, Lab Workers Should Get Japanese-Encephalitis Vaccine

By Will Boggs MD

July 25, 2019

NEW YORK (Reuters Health) - Travelers to high-risk areas and laboratory workers who could be exposed to Japanese-encephalitis (JE) viruses should receive the JE vaccine, according to updated recommendations from the Advisory Committee on Immunization Practices (ACIP).

"The decision about whether to vaccinate should be individualized and consider the 1) risks related to the specific travel itinerary, 2) likelihood of future travel to countries where JE is endemic, 3) high morbidity and mortality of JE, 4) availability of an effective vaccine, 5) possibility (but low probability) of serious adverse events after vaccination, and 6) the traveler's personal perception and tolerance of risk," Dr. Susan L. Hills of the National Center for Emerging and Zoonotic Infectious Diseases, Centers for Disease Control and Prevention (CDC), in Fort Collins, Colorado, told Reuters Health by email.

In a paper published July 19 in Morbidity and Mortality Weekly Report (MMWR), Dr. Hills and colleagues summarize the epidemiology of JE virus, describe the vaccine that is licensed and available in the U.S., and provide recommendations for its use among travelers and laboratory workers.

JE, a mosquito-borne virus, occurs throughout most of Asia and parts of the Western Pacific. As many as 30% of infected individuals die and 50% can have neurologic, cognitive, or behavioral sequelae.

The inactivated Vero cell culture-derived JE vaccine (JE-VC) is the only JE vaccine licensed and available in the U.S., and there is no available antiviral treatment for JE virus infection.

In endemic areas, JE virus transmission occurs primarily in rural agricultural areas, where it is spread by infected mosquitoes and not from person to person through direct contact.

"Most travelers to countries where the disease is endemic are at very low risk for JE, with the overall incidence of JE among persons from non-endemic countries who travel to Asia estimated to be less than one case per 1 million travelers," Dr. Hills said.

"However, some travelers are at increased risk for infection on the basis of their travel plans. Factors that increase the risk for JE virus exposure include 1) traveling for a longer period; 2) travel during the JE virus transmission season; 3) spending time in rural areas; 4) participating in extensive outdoor activities; and 5) staying in accommodations without air conditioning, screens, or bed nets," she said.

Healthcare providers should assess each traveler's risk for mosquito exposure and JE virus infection on the basis of their planned itinerary and discuss ways to reduce their risk.

ACIP recommends JE vaccine for persons moving to a JE-endemic country to take up residence, longer-term travelers to JE-endemic areas (one month or more), frequent travelers to JE-endemic areas, and possibly for shorter-term travelers with an increased risk for JE based on the risk factors above.

Vaccination is also recommended for all lab workers with a potential for exposure to JE viruses other than the SA14-14-2 JE vaccine virus.

In contrast, the vaccine is not recommended for travelers with very low-risk itineraries, such as shorter-term travel limited to urban areas or travel that occurs outside of a well-defined transmission season (mainly summer and fall).

Pregnancy is a caution for the use of JE-VC, and vaccination should usually be deferred because of a theoretical risk for the developing fetus.

"While the document's purpose is to provide information and recommendations on JE vaccination for U.S. travelers, it should be remembered that JE virus is an important problem for local populations living in JE-endemic areas in Asia and the Western Pacific," Dr. Hills said. "JE virus is the leading vaccine-preventable cause of encephalitis in Asia, and a substantial cause of life-long disability. A 2011 systematic review of JE disease burden estimated that approximately 68,000 cases occur each year."

"The World Health Organization recommends integration of JE vaccination into national immunization schedules in all areas where the disease is a public health priority, and substantial progress has been made in establishing and strengthening JE immunization programs during the last 15 years," she said. "However, because JE virus is maintained in an enzootic cycle between animals and mosquitoes, disease elimination is not possible, and ongoing efforts and attention will need to ensure ongoing sustainability of JE control to reduce the impact of this disease in endemic areas."

Dr. Young-Min Lee from Utah State University, in Logan, who studies JE-virus (JEV) infection, told Reuters Health by email, "Outside the currently defined boundaries of JEV activity in Asia and the Western Pacific region, JEV genomic RNA/proteins were detected in Italy from tissue samples of both healthy and dead birds in 1997-2000, as well as from a pool of mosquitoes in 2010. Also, a resident in Angola was found to be locally co-infected with JEV and yellow fever virus in 2016. These pieces of recent evidence therefore indicate that JEV is circulating not only widely in the Asia-Pacific region but also possibly locally in Europe and Africa, with the potential for further spread."

"JEV is not introduced in the U.S. yet, but the likelihood of JEV being introduced into this country is considerable," said Dr. Lee, who was not involved in the new recommendations. "Currently, West Nile virus and St. Louis encephalitis virus (two other viruses closely related to JEV) are circulating in the U.S. The situation will be complicated if JEV emerges in this country. Therefore, physicians should be aware of our currently available options to prevent JEV infection."


MMWR Morb Mortal Wkly Rep 2019.