First dengue vaccine trial disappoints

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http://www.sciencenews.org/view/generic/id/345037/title/First_dengue_vaccine_trial_disappoints

A long-awaited first test of a vaccine against dengue fever has failed to consistently prevent the viral disease in children, researchers report online September 11 in the Lancet. The mixed results have left scientists wondering how one form of the virus dodged what looked like a potent immunization regimen.

The shaky showing in Thai children won’t send scientists back to the drawing board, since the vaccine is already being tested extensively elsewhere. Officials at vaccine maker Sanofi Pasteur even point out that the vaccine engendered respectable defense, protecting against three of the four viral subtypes of dengue in 61 to 90 percent of vaccinated children.

But the vaccine failed to fend off one subtype of dengue, called dengue serotype 2. That subtype is common in the region of Thailand where the trial was conducted. What’s more, the specific version of the dengue subtype 2 in that area turned out to be particularly aggressive, says study coauthor Nadia Tornieporth, a physician and head of global clinical research at Sanofi Pasteur U.S. headquarters in Swiftwater, Pa.

“This trial is a cautionary tale for investigators designing future dengue vaccine trials,” says Scott Halstead, a physician at the International Vaccine Institute in Seoul, Korea, writing in the same issue of Lancet. Most of the children in the study had previous exposure to a dengue subtype or a related virus, a situation that makes it difficult to establish the effectiveness of the new vaccine, he says.