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Trial Shows Vaccine Effective Against Most Dengue Viruses

Mosquito (Germán Meyer)A clinical trial by researchers from the pharmaceutical company Sanofi Pasteur, with clinicians and public health officers from Thailand, shows a candidate vaccine to prevent the tropical disease dengue fever was effective against three of the four dengue viruses. The findings from the trial, funded by the Dengue Vaccine Initiative, appear online in the journal The Lancet (paid subscription required).

Dengue fever is a disease caused by four related viruses, identified as DEN 1, 2, 3, and 4. The viruses are transmitted to humans by the Aedes aegypti mosquito, but the disease is carried by humans that often serve as the source of the virus to uninfected mosquitoes. Most cases occur in tropical or sub-tropical areas of Asia or Latin America. The Dengue Vaccine Initiative says some 2.5 billion people are at risk of the disease resulting in 21,000 deaths per year.

This disease when transmitted to humans can be asymptomatic or mild at first, but can lead to severe forms of the disease characterized by hemorrhage, shock, coma, and death, with fatality rates exceeding 20 percent. The only treatments for dengue address symptoms of the disease, not the underlying causes, nor is there a vaccine to prevent infection.

The phase 2 trial tested a vaccine candidate made by Sanofi Pasteur, called CYD-TDV, on 4,002 schoolchildren in Thailand, age 4 to 11, where dengue is known to be widespread. The sample was randomly divided into test and control groups, with 2,669 children in the test group, and 1,333 in the control group. The test group received three injections of CYD-TDV, while the control group received three injections of either a rabies vaccine or a placebo.

The results indicate CYD-TDV was 61 to 90 percent effective against three of the four dengue viruses — DEN 1, 3, and 4 — compared to the control, but not DEN 2 that appears resistant to the vaccine. The authors of the paper say the vaccine was well-tolerated by the trial participants, with no safety issues reported about two years after the first dose.

Dengue Vaccine Initiative says there are three other vaccine candidates in various stages of development. Sanofi says more extensive and potentially conclusive phase 3 clinical trials are underway in Latin America (Mexico, Colombia, Honduras, Puerto Rico and Brazil) and in Asia (the Philippines, Vietnam, Malaysia, Indonesia, and Thailand). In addition, the U.S. Food and Drug Administration has given fast-track designation for the vaccine, because it addresses an unmet medical need for a serious disease.

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Photo: Germán Meyer/Flickr

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