Ebola experimental drugs and vaccines

No treatments for Ebola have been proven in human trials, but the World Health Organization says the experimental drugs being developed can be used under limited circumstances.

The UN health agency's panel of medical experts reached a consensus, saying it's ethical to offer unproven interventions, given the size of the outbreak in West Africa, with caveats.

"There are some potential therapies and vaccines which look promising, but which have not yet been tested, or if they have, not thoroughly in clinical trials," said Marie-Paule Kieny, the WHO's assistant director general for health systems and innovation.

"Some of these, as you know, have already been used, or others are currently considered for compassionate use."

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Kieny stressed it's important "to not give false hope to anybody that Ebola can be treated now. This is absolutely not the case."

The Ebola virus has killed more than 11,000 people in Guinea, Sierra Leone and Liberia. It took a full year after the Ebola outbreak was reported for the first large-scale tests of potential vaccines to start. As new cases declined, plans for clinical trials to test experimental Ebola vaccines have been scaled back.

"There's no doubt everybody is very happy we have so few Ebola cases, but obviously it's also a bit disappointing — when there was so much effort and energy put into accelerating the vaccines — that there are suddenly no cases for the trials," Kieny said in June 2015.

Mapp Biopharmaceutical's ZMapp experimental treatment is a combination or cocktail of three monoclonal antibodies that is designed to bind to the protein of the Ebola virus, neutralizing the virus so it can't do any further damage.

The drug resulted from a collaboration between Mapp Biopharmaceutical, LeafBio, Defyrus, the U.S. government and the Public Health Agency of Canada. It is grown in tobacco plants.

Dr. Michael Osterholm, director of the Center for Infectious Disease Research and Policy, teaches at the University of Minnesota in Minneapolis.

"What we need to do between now and the next several months is really concentrate on the heart of what is going to save lives. We are not going to save that many lives with drugs even if they work. We're going to save lives by preventing infections from occurring," Osterholm said in an interview with CBC's Radio's The Current. 

Several treatments have been proven to work in non-human primates such as rhesus macaques, but they haven't been tested in humans to be licensed as proven safe and effective treatments, Kieny said.

Individuals who are dying or their family members may be willing to try an experimental treatment, Osterholm acknowledged.

Since informed consent is needed, some experts say it's reasonable to offer the drugs to health-care workers who understand the potential risks and benefits.

On a societal level, offering the drug to individuals isn't the way to go about testing, Osterholm said.

The CDC's website says two other companies, B.C.-based Tekmira and Biocyst Pharmaceuticals, have received funding from the U.S. Department of Defence. Both companies also have therapeutic candidates for Ebola.

Tekmira's experimental drug, TKM-Ebola, targets Ebola's genetic material. The experimental drug is known as an RNA interference therapeutic. In June 2015, Tekmira announced the end of a clinical trial on TKM-Ebola in Sierra Leone, on the grounds that "continuing enrolment was not likely to demonstrate an overall therapeutic benefit."

Biocyst Pharmaceuticals' experimental drug, BCX4430, prevented infection from another hemorrhagic virus, Marburg virus, in non-human primates, a 2014 study in Nature suggests.

Canadian research

Up to 50,000 doses of another potential Ebola drug are ready to be used in West Africa, a Canadian researcher says.

Eleanor Fish, an immunologist and senior scientist at Toronto's University Health Network, co-wrote a study on a synthetic version of interferon, a molecule the body makes to fight viruses, to treat patients with SARS in the city in 2003.

Fish's drug has been tested against Ebola virus in guinea pigs and mice.

Siga Technologies is also working on a potential treatment.

Meanwhile, several potential vaccines to prevent Ebola infection are also undergoing tests. Unlike drugs that are meant to be given after exposure, vaccines are generally designed to help prevent infection.

Experimental vaccines

One experimental Ebola vaccine was also partly developed at Canada's National Microbiology Lab.

Normally, vaccines are given before exposure to a virus. The Canadian vaccine, called VSV-ZEBOV, is so robust that it could also work as a treatment, said Gary Kobinger, who heads the special pathogens program at Canada's National Microbiology Lab in Winnipeg.

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"The vaccine is extremely potent and stimulates an immune response to protect an individual against the virus, and if that immune response is so fast to establish itself that the individual is protected by the time that the virus keeps growing," said Kobinger. "If you want, it's a race and then the vaccine wins the race."

It's also possible that the vaccine competes with the Ebola virus for target cells where the virus is copied, Kobinger said.

Another experimental vaccine developed at the U.S. National Institute of Allergy and Infectious Diseases (NIAID) and licensed by GlaxoSmithKline cleared its Phase 1 trial for safety. That vaccine includes genetic material from the virus.

"You don't inject the entire virus of Ebola because that would be dangerous," said Dr. Anthony Fauci,  director of NIAID. "So what you do is get a very small component of  the virus, which is a protein that coats the outside of the virus."

Fauci's institute describes a Phase 2/3 clinical trial to evaluate the safety and efficacy of both the Canadian VSV-ZEBOV investigational Ebola vaccine and the NIAID/GSK investigational Ebola vaccine.

"Demonstrating the efficacy of vaccines is even more complex than drugs because it involves finding people who are exposed [and] comparing them to people who are exposed," said James Lavery, who studies research ethics at the Li Ka Shing Knowledge Institute of St. Michael's Hospital in Toronto.

Lavery said it might make sense for experimental vaccine studies to focus on those at high risk, such as health-care workers or people who would be involved in burials or those in proximity to patients who are being cared for or dying.

"You are very likely to learn nothing about the efficacy of the vaccine, in which case, it's a humanitarian gesture, but it may add nothing to our understanding of how these vaccines may work in future outbreaks."

Vaccines normally take years to move through all clinical testing before they are licensed for use.