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Evaluating the safety of Japanese encephalitis vaccines

Patient w/vaccine bandaid | Image credit: CDC

A recent scientific study evaluated the safety of Japanese encephalitis vaccines.[1] In the U.S. only the Valneva Ixiaro vaccine is used so we'll focus on that for our review of this work.

Japanese encephalitis definition

Japanese encephalitis is a viral disease that is mostly endemic to the Asia-Pacific region with mortality rate

of approximately 30%. Long-term neurological, cognitive and psychiatric issues develop in about 50% of

survivors. There is no available antiviral therapy for Japanese encephalitis.

Japanese encephalitis vaccine

Japanese encephalitis vaccines play a major role in preventing this terrible disease. The incidence of Japanese encephalitis declined over years and the age distribution shifted toward adults in countries where Japanese encephalitis immunization program exists.

Safety of the Japanese encephalitis vaccine

The Japanese encephalitis vaccine is an inactive vaccine, meaning there is no live virus that can get you sick but your own body's immune reaction can make you feel sick.

Common adverse reactions include injection site reactions and fever, and severe adverse reactions are


Solicited adverse events were mild with 44.7% of injection site tenderness, 26.2% of injection side erythema, and 1.1% of fever. In one study with enrollment of both adults and children in the USA, the reporting rates of adverse events and serious adverse events following immunization were 14.8 and 1.1 per 100,000 doses distributed, respectively.[1]

Concluding thoughts

The Japanese encephalitis vaccine is very safe. It is also very effective. If you have plans to travel to India, Asia, Indonesia, Australia or other affected areas, you should talk to a travel health specialist before you go.


1. Hu, Y. L., & Lee, P. I. (2021). Safety of Japanese encephalitis vaccines. Human Vaccines & Immunotherapeutics, 17(11), 4259-4264.


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