An experimental dengue vaccine worked almost perfectly in a small trial in which volunteers were deliberately given a mild form of the disease, scientists said last week.
The results in 41 volunteers were so encouraging that they justified starting a larger trial, now underway in Brazil. The vaccine was jointly developed by the National Institute of Allergy and Infectious Diseases, and the Food and Drug Administration.
In the study, published in Science Translational Medicine, 41 volunteers were given the vaccine, now named TV003, or a placebo.
Six months later, all were “challenged” — deliberately infected — with a genetically modified strain of dengue virus from Tonga that can cause only mild disease.
No replicating virus was found in the blood of any of the 21 volunteers who received the vaccine. Dengue was found in the blood of all 20 who had the placebo, and many developed signs of infection, such as rashes and low levels of white blood cells.
There are four dengue viruses, or serotypes, all spread by Aedes aegypti, the mosquito that spreads the Zika virus.
Every year, nearly 400 million people around the world get dengue. Most recover and become immune to the first serotype they had.
But about 2 million who later become infected with a different serotype develop dangerous hemorrhagic fevers, and about 25,000 die from them each year.
One of several dengue vaccines in development, Dengvaxia, has recently been licensed in Mexico. But it offers relatively little protection against some serotypes and may make some young children who receive it more likely to be hospitalized years later.
“Dengue is unique, and if you don’t do it right, you can do more harm than good,” said Dr. Anna P. Durbin, a researcher at Johns Hopkins Bloomberg School of Public Health who led the testing of TV003.
Because dengue is from the same family as the Zika virus, the techniques used to make TV003 might be applicable to a Zika vaccine, she said.