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."

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

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.

ZMapp was given to two American health workers infected with Ebola in Liberia.

The last of the drug is on its way to Liberia for two stricken doctors, according to a U.K.-based public relations firm representing Liberia.

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.

"The available supply of ZMapp has been exhausted," Mapp Biopharmaceutical’s website said Tuesday. The company said it complied with every request for the drug that had the necessary legal and regulatory authorization and that the drug was provided for free.

It could take several months before more doses are available, said Dr. Michael Osterholm, director of the Center for Infectious Disease Research and Policy, who 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.

Tekmira Pharmaceuticals

Based in Burnaby, B.C., Tekmira Pharmaceuticals has been developing an anti-Ebola therapeutic called TKM-Ebola. (Tekmira/Google profile)

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

"The data are so limited that it's to the point of where this is a really crapshoot. It's not an experiment. There's not sufficient drugs to even look at this, nor is there the conditions on ground in Africa to be able to study this systematically to find out, are people actually doing better with the drug or not."

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 U.S. Food and Drug Administration halted a small safety study with questions about a reaction in healthy volunteers, but last week Tekmira announced that the FDA had modified its restriction. The FDA change means the experimental drug, known as an RNA interference therapeutic, could potentially be used on people infected with Ebola, the company said.

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.

Again, none have been tested on humans.

Experimental vaccines

One experimental Ebola vaccine was also partly developed at Canada’s National Microbiology Lab. Canada is in discussions with other countries and the World Health Organization about sending doses of the vaccine to West Africa, a spokesman for Health Canada says.

Normally, vaccines are given before exposure to a virus. The Canadian vaccine, called VSV-BOV, 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.

"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.

hi-gary-kobinger-120823

Since the Canadian experimental vaccine against the Ebola virus is extremely potent, tests in lab animals suggest it could work as a treatment, says Gary Kobinger of the National Microbiology Lab. (CBC)

Another experimental vaccine developed at the U.S. National Institute of Allergy and Infectious Diseases (NIAID) and licensed by GlaxoSmithKline is expected to begin first-stage safety studies sometime in the fall. 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."

The U.S. Centers for Disease Control and Prevention lists two other potential Ebola vaccines in development. Another experimental vaccine from Johnson & Johnson's Crucell unit should enter phase 1 clinical trials in late 2015 or early 2016. Profectus Biosciences is also working with U.S. scientists on another preclinical 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.

With files from CBC's Karen Pauls, Daniel Schwartz and Reuters