Waning Immunity to Japanese Encephalitis May Increase Dengue Severity

scientists from Duke-NUS Medical School, working wiht researchers in Nepal, have discovered that decreasing immunity to Japanese encephalitis virus (JEV) could raise the risk of more severe dengue disease. Published in science Translational Medicine, the study demonstrates how protection from one virus can unintentionally influence the body’s response to another.

Japanese encephalitis is a serious illness, causing death in about 25% of those with severe symptoms and leaving many survivors with lasting disabilities. dengue is also a meaningful public health issue, being the fastest-growing mosquito-borne viral disease globally. It can cause severe illness and even death, with cases rapidly increasing in Nepal. Fortunately, japanese encephalitis is preventable with vaccination, and Nepal has made considerable progress through mass immunization. Dengue prevention, though, largely relies on mosquito control and personal protection. While JEV vaccination initially creates high antibody levels, immunity can diminish over time, particularly without booster shots.

Researchers analyzed over 500 patients in Nepal over five years – a unique location where both JEV and dengue are actively spreading. They found that individuals previously vaccinated against JEV, but with declining antibody levels, were more prone to experiencing severe dengue symptoms. Those who maintained strong JEV immunity weren’t affected.

We chose Nepal as a study site because it’s one of the few countries where dengue is spreading quickly in a population that already has widespread immunity to another flavivirus, Japanese encephalitis. This gave us a unique chance to see how prior immunity shapes dengue illness, and we found that people whose Japanese encephalitis immunity had waned were more likely to become severely ill from dengue.

Dr. Sidharth Malhotra, of the programme in Emerging infectious