As Canada prepares to ship out as many as 1,000 doses of an experimental Ebola vaccine, it is also preparing to hand off to international medical experts the gut-wrenching decisions about who in West Africa will receive an injection that could protect against the deadly virus – or cause unanticipated and dangerous side effects.
Here is an explainer behind the vaccine:
Perhaps the most widely mentioned drug during the current Ebola outbreak is a serum developed by a San Diego-based company called Mapp Biopharmaceutical Inc.
The drug, called ZMapp, is a still-experimental Ebola treatment that functions in a similar way to some vaccinations. Usually, vaccinations work by exposing the body to a small quantity of some virus, prompting the immune system to produce antibodies. However, in the case of especially aggressive and fast-moving diseases such as Ebola, that process can be too time-consuming. Instead, ZMapp delivers the antibodies directly to the body. The drug is a cocktail of three antibodies – two of which latch on to the virus and attack it directly, while the third one alerts the immune system to the presence of the virus. In early trials, ZMapp has shown positive results. Perhaps most important, the drug also has a relatively wide window of effectiveness. In animal studies in Winnipeg, the drug was administered to non-human primates that had been infected between one and three days earlier – with very successful results, according to Erica Ollmann Saphire, a professor with the California-based Scripps Research Institute and an expert on viral hemorrhagic fever pathogenesis. Indeed, even in some cases where the disease had progressed to the hemorrhagic fever stage, some subjects could still be saved.
Another potentially effective treatment for the Ebola virus is being developed by a pharmaceutical company called Tekmira Pharmaceuticals Corp., based in Burnaby, B.C.
The drug, called TKM-Ebola, attacks the genetic material of the virus – and while testing is still far from complete, it has shown positive results.
For years, Tekmira worked on the drug in association with researchers at Boston University, and using research funding provided in part by the U.S. Department of Defense as part of a $140-million contract.
The basis of the treatment is a mechanism called Ribonucleic acid interference, or RNAi. Drugs based on RNAi try to shut down genes responsible for certain disease. The RNAi mechanism itself has been well-studied by biologists for years. To produce the Ebola drug, however, Tekmira combined the RNAi treatment with its proprietary mechanism designed to deliver the treatment to disease sites.
In early-stage testing, the drug showed significant potential. In a preclinical study published in The Lancet, researchers found that non-human primates could be protected from an otherwise lethal dose of the virus using the TKM-Ebola treatment.
An Ebola vaccine, generally, functions in a manner similar to many other vaccines. In essence, the body is given a small taste of the virus. This prompts the immune system to produce antibodies to fight the small infection, and as a result the subject is protected from full-blown iterations of the virus in the future.
There are myriad researchers in the U.S. and Canada working on such vaccines, and many have shown signs of progress. In one study completed by an American pharmaceutical company, animals given an Ebola vaccine before the onset of infection had a 100-per-cent protection rate. In some cases the vaccine managed to stop the virus even when administered shortly after an infection.
But because the vaccines have had almost no testing at all on human subjects, it is unclear whether the promising results will translate. A vaccine would also be of slightly limited use, compared with other treatments, in helping those stricken during the current Ebola outbreak, in part because it is often difficult to determine when a patient was infected, and the vaccine’s effective window of treatment appears to be smaller than that of drugs such as ZMapp.