At least 15 Ebola vaccinations are being tested or developed, but as the rate of new infections drops, clinical trials could be
As scientists and medical experts race to develop a vaccine to stop the spread of Ebola, there are concerns the window of opportunity may be closing.Wary of a persistent virus and pockets of resistance to emergency health measures, experts warn against premature predictions of an end to the deadly epidemic.
But the rate of new infections has plummeted. Fewer than 100 cases per week, on average, are now being reported across West Africa, down from a peak of 1,000 last fall.
That decline, though welcome, could jeopardize the large clinical vaccine trials now under way.“You cannot test a vaccine for Ebola if there’s no Ebola,” says Dr. Charlie Weller at the Wellcome Trust in the U.K., which hasprovided about $20 million in funding for vaccines, treatments and research.
“You need an active epidemic, which is why there has been such a global collaborative effort to start these (vaccine) trials as quickly as possible.” The Ebola epidemic has wreaked havoc in West Africa, killing more than 10,000 people and devastating parts of Liberia, Sierra Leone and Guinea.
Enormous resources are being mobilized to come up with a vaccine: at least 15 are being tested or developed in hospitals and clinics in West Africa, North America, Western Europe, Russia and China.
The World Health Organization has identified two as being most advanced: VSV-ZEBOV, first developed by researchers at Winnipeg’s National Microbiology Laboratory; and ChAd3-ZEBOV, developed by the U.S. National Institute of Allergy and Infectious Diseases (NIAID) and pharmaceutical company GSK.
Last Wednesday, scientists published the first results of clinical trials carried out in the U.S., Gabon, Kenya, Germany and Switzerland in the New England Journal of Medicine. They reveal that a single dose of the Canadian-made VSV-ZEBOV vaccine is safe and effective in producing antibodies that ward off the Ebola virus. (Some volunteers experienced minor side-effects such as joint pains, a rash or fever lasting an average of 11 days.)
Having shown promise in hospitals and laboratories, the vaccines’ real test will be in the field. Trials are now under way in West Africa, the epicentre of the Ebola epidemic.
In Guinea, some 10,000 people will receive an injection of VSV-ZEBOV in a massive clinical trial underway there by the government and international partners, including the WHO. The patients will be followed for three months and the results could be available as early as July.
Medical practitioners will use what is known as the “ring vaccination” strategy: inoculating the infected person, tracking down all of the people with whom they’re in contact and vaccinating each of them in turn if they consent.
This tracing strategy helped eradicate smallpox in the 1970s, and many hope it will slow to a halt an Ebola epidemic that has infected more than 25,000 people across West Africa since the first cases were confirmed in Guinea in March 2014.
In addition, both leading Ebola vaccines are being tested in Liberia in trials that began in February. Volunteers are assigned at random to receive a single injection of either chAd3-ZEBOV, the VSV-ZEBOV vaccine or a placebo.
With a death toll of more than 4,300, Liberia has been hardest hit by the epidemic. But the country has reported a sharp drop in new cases — with just one new infection in the past five weeks.
Scientists overseeing the trials are now considering expanding to sites in neighbouring Guinea, where there are larger caseloads.
In the rush to find a vaccine that works though, some fear they won’t finish testing in time.
“In terms of whether we’re likely to get a licensed drug or vaccine during this outbreak, it looks unlikely,” said professor Jonathan Ball, a virologist at the University of Nottingham. But with Guinea and Sierra Leone still reporting dozens of new cases every week and preliminary test results expected this summer, there may still be time for a successful vaccine to emerge — if not for this outbreak, then for the next one.
“We still have lots of evidence to suggest that (one of the vaccines) might work, and therefore hopefully we will be better prepared in any future outbreak to actually get clinical trials up and running much faster,” added Ball. For Dr. Jean-Paul Jemmy of Médecins Sans Frontières, which sounded the alarm on Ebola last year, the danger remains.
“Not having an efficacious vaccine will leave you in a situation where you can still have an outbreak that will flare up and be just as damaging for the affected population,” he said. “But we have learned a lot during this outbreak. And there are a number of (anti-Ebola) products in the pipeline.”
One vaccine candidate, cAd3-EBOZ, uses a chimpanzee-derived cold virus to deliver Ebola virus genetic material from the Zaire strain of virus causing the outbreak in Liberia.
The other candidate, VSV-ZEBOV, employs vesicular stomatitis virus, an animal virus that primarily affects cattle, to carry an Ebola virus gene segment. The VSV-ZEBOV vaccine was developed by the Public Health Agency of Canada and licensed to NewLink Genetics Corp. through its wholly owned subsidiary BioProtection Systems Corp.
Published: Sun Apr 05 2015. By Kyle G. Brown
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