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An experimental Ebola vaccine looks promising in a human trial

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It was made by introducing an Ebola gene in a chimpanzee cold virus

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An Ebola vaccine produced using a chimpanzee common cold virus appears to be safe to use on humans, according to a study published today in the New England Journal of Medicine. Three different doses of vaccine were tested on healthy humans in the UK, and it was well-tolerated; it triggered high levels of antibody formation without also triggering serious side effects. But until the vaccine is tested in an area where an Ebola risk actually exists, it’s efficacy against the disease will remain a mystery.

The current outbreak has claimed the lives of over 22,000 people

Since the beginning of the West African outbreak, Ebola has claimed the lives of over 22,000 people. There’s no cure for Ebola, but it can be controlled through routine hand-washing and by using gloves and other barriers to prevent contact with infectious bodily fluids. It doesn’t spread through the air; only direct contact with the body fluids of a person who is showing symptoms of Ebola will spread the disease. Still, the death toll from Ebola has been devastating, and researchers are actively searching for a way to protect people from becoming infected.

In the study, researchers tested three different doses of the vaccine for safety and tolerability. They did so by giving a single dose to 60 healthy participants in Oxford, UK. Then, the researchers monitored the patients for four weeks. During that time, they measured the participants’ immunological responses to the vaccines and checked for negative reactions. The vaccine didn’t raise any safety concerns, and only two people developed fever in its aftermath.

"They showed that there’s a good immune response."

"They showed that there’s a good immune response," says Kirsten Lyke, an Ebola vaccine researcher at The University of Maryland who didn’t participate in the study. It triggered the production of a high level of antibodies, she says, and "it seems pretty safe."

The vaccine used in this study was made by isolating a chimpanzee cold virus that doesn’t cause illness in humans. Researchers deleted genetic material from the virus to prevent it from reproducing in humans after vaccination. Then, they introduced a gene from the Ebola virus into the cold virus. This change causes the virus to use a patient’s cells to synthesize an Ebola protein belonging to the Zaire strain, the strain currently raging in West Africa, upon vaccination. When that happens, the protein is recognized by the human immune system as something to combat, and the body responds by producing T cells and antibodies that researchers hope will be enough to fight the Ebola virus should exposure ever occur.

This isn’t the only Ebola vaccine undergoing testing. There are several other vaccines being tested for safety at the moment, including a similar one that expresses two forms of Ebola proteins — one from the Zaire strain and one from the Sudan strain. "This means that potentially protective vaccines could be available to health care workers in the field within clinical trials to assess vaccine efficacy" in the near future, says Katie Ewer, an immunologist at The University of Oxford and a co-author of the study.

"Efficacy can only be tested in the context of exposure to the outbreak in West Africa."

Now that this trial is over, Ewer and her team hope to try to improve the immune responses they’ve seen by introducing a second vaccine made from a modified vaccinia Ankara virus — a virus that was used to make the smallpox vaccine — and using it as a booster dose. The results of that study should be published in the coming months, Ewer says. Of course, the most important step is to test the vaccine in an area where people are actually at risk for Ebola. "Efficacy can only be tested in the context of exposure to the outbreak in West Africa," she says.

Until that happens, all researchers can do is test vaccines for safety and compare the immunological responses seen in humans to those of vaccinated chimps exposed to Ebola. "The next step is to ask 'does it actually protect against Ebola?'" Lyke says. But "at least humans are mounting good immune responses" in the meantime.