It’s called a “human challenge.”

Volunteers allow researchers to inject them with a virus in order to test experimental vaccines.

“What we’re trying to do is accelerate vaccine research,” said senior author Dr. Anna Durbin of Johns Hopkins University’s School of Public Health. “[In order] to know if you have a stinker  you try to test it in thousands or tens of thousands of people.”

The little-known but increasing type of research was successful with volunteers who let researchers inject them with the dengue virus -- a mosquito-borne flavivirus with symptoms that include severe joint and muscle pain, fatigue, nausea, vomiting and skin rash -- as the experimental vaccine protected them.

While most people survive dengue with few or even no symptoms, more than 2 million a year suffer serious illness and about 25,000 die. Researchers at John Hopkins and the University of Vermont gave 41 healthy people either a single does of the experimental vaccine or a dummy shot. Six months later, they were all injected with the dengue-2 strain.

All 21 volunteers who received the vaccine were protected, but the other 20 had dengue virus in their bloodstream.

The human challenge works to prevent outbreaks by deliberately infecting healthy people in the quest for new or improved vaccines against a variety of health threats, from flu to malaria.

Now scientists want to use the same research with the Zika virus, known as dengue’s cousin.

“We see a Zika challenge model as really beneficial for not only vaccine development but also to learn more about Zika itself,” Durbin said.

However, she did add, “We know very little about Zika right now.”

(Photo: Klaus Tiedge/Blend Images/Corbis)