Ebola vaccine cAd3-EBO raises hopes in first trial | Science| In-depth reporting on science and technology | DW | 27.11.2014
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Ebola vaccine cAd3-EBO raises hopes in first trial

Good news has been rare when it comes to the Ebola outbreak. Now, there's a glimmer of hope. One vaccine has yielded promising results in humans - even if it has its drawbacks.

For months, bad news - even bordering on the apocalyptic - was the norm when it came to Ebola in West Africa: Exponential infection rates, agonizing deaths, and an epidemic lasting much longer than expected.

For those waiting anxiously for a sign of hope, maybe - just maybe - here it is.

In September, human trials began on Ebola vaccine candidates. Now, the first results have been published on the website of "The New England Journal of Medicine."

"The experimental vaccine was well tolerated and produced immune system responses in 20 out of 20 healthy adults who received it," announces the National Institute of Allergy and Infectious Diseases (NIAID) in Bethesda, Maryland, which co-conducted the study with the pharmaceutical company GlaxoSmithKline.

This does not mean, however, that the vaccine protects against the deadly virus.

This study is only a first step - an important one, experts say - and it means researchers can now start crucial, real-world testing in West Africa on people who come into contact with the virus.

Chimp cold with a dash of Ebola

Two completely different vaccine candidates are currently being tested on humans.

The vaccine results announced Wednesday (27.11.2014) name complicated name cAd3-EBO. It consists of a chimpanzee-derived cold virus with genetic Ebola material inserted inside it.

The vaccine actually comes in two varieties: Half of the cold viruses contain gene material from the Ebola Zaire-Guinea varient responsible for the recent outbreak in West Africa, while the other half is from a Sudan strain.

Crucially, each candidate vaccine does not contain a complete Ebola virus, therefore rendering it incapable of causing the disease.

Ebola vaccine Photo: REUTERS/Public Health Agency of Canada

Another vaccine was developed by the Public Health Agency of Canada - results of human trials are still pending

Antibody production

Twenty healthy adult volunteers from the Washington D.C. area received one shot of the experimental vaccine.

Ten recipients received a low vaccine dose, the other 10, tenfold that amount.

After four weeks, all volunteers had produced antibodies against at least one of the two different Ebola species.

"No safety effects were identified," the researchers write in their report.

Two volunteers, though, developed a fever which was only transient, the researchers say.

That no volunteer developed serious side effects "is very good news," said Cesar Munoz-Fontela, a researcher at the Leibniz Institute for Experimental Virology in Hamburg.

He stresses that it is still a preliminary report and that it's difficult "to draw a lot of conclusions." But, according to Munoz-Fontela, the candidate vaccine seems "promising."

That two patients developed a fever won't be a problem, he says, adding that "there are a lot of vaccines that cause mild fevers in vaccinees."

Airbus A340-300 plane called Robert Koch Photo: TOBIAS SCHWARZ/AFP/Getty Images

While researchers are working on a vaccine, German engineers constructed an aircraft with a special isolation cabin for Ebola-infected passengers

Animals reacted differently

Not everything went perfectly, however.

All volunteers produced antibodies - which, according to Munoz-Fontela, is "quite nice."

But researchers expected this vaccine would also induce a T-cell response in the volunteers. These cells are an important part of the immune system.

"We know from previous studies in non-human primates that CD8 T cells played a crucial role in protecting animals that had been vaccinated […] and then exposed to otherwise lethal amounts of Ebola virus," said Julie Ledgerwood of NIAID, the trial's principal investigator.

Of the 20 volunteers in the human trial, though, only two in the lower-dose group and seven in the higher-dose group produced these CD8 T cells.

"If this vaccine depends on CD8 T cell response, this may be a problem," says Munoz-Fontela.

Munoz-Fontela is part of a research team that plans to have a closer look at people who were infected with the Ebola virus and who survived the disease.

The immune response of these survivors could give better insight into how a good Ebola vaccine might work in humans.

Ebola survivors Photo: Julius Kanubah

People like Oldlady Kamara who have survived Ebola might help in developing a vaccine

Still a long way to go

At this point, there is no way to know from the results of the phase-one study if the vaccine will protect people in the field, experts say.

First of all, researchers are waiting for further results: Another version of the same vaccine is being tested at the University of Maryland in Baltimore. That version of the vaccine also consists of the chimpanzee-cold virus as a carrier, but rather than carrying the genetic material from two Ebola species, it contains only the Zaire-Guinea variety.

The results will be available by the end of this year.

"If the combined data from these trials are positive, the next phases of the clinical trial program will begin in early 2015," GlaxoSmithKline announced, "to see whether the immune response we are seeing in phase one actually translates into providing people in affected countries with meaningful protection against Ebola."

If it does, we can speak of very good news indeed.

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