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Some caution with the good news about an Ebola vaccine

A nurse prepares measles vaccine injection at the Madina Health Center, Guéckédou, Guinea. (Credit: UNICEF Guinea)

The early results from an Ebola vaccine trial in Guinea show it to be 100 percent effective against the virus. It is  good news after more than 11,000 people died in West Africa over an 18-month period. But there are questions about the trial’s methodology and the rush to vaccinate in the hard-hit areas that make it tough to prove that the vaccine deserves the credit for people not getting sick – important questions that regulators must address before approving the vaccine.

The trial in Guinea tested the single-dose rVSV-ZEBOV, which was created by researchers working at the Public Health Agency of Canada. It included 7651 people, randomly split into two groups. Groups were created based around families and friends close to infected individuals. The first group was vaccinated immediately and the second group three weeks later. In the first group, there were no Ebola infections 10 days after vaccination. In the delayed group, 16 cases of Ebola developed, but there were no cases six days after vaccination. There was no control group of people not receiving the vaccine.

Results of the trial were published late July in the British health journal The Lancet. The 100 percent effectiveness of the vaccine in the first group showed the promise that the vaccine could prevent Ebola infections and deaths. Doctors Without Borders, the head of the World Health Organization and some health experts championed the news as a major achievement.

“These Ebola vaccine results are a huge achievement, showing that it is possible to test experimental vaccines in the context of an epidemic, under the most difficult conditions,” wrote Jeremy Farrar, director of the Wellcome Trust, which helped fund the study, in the Guardian. “They demonstrate the power of equitable international partnerships and flexibility, and should change how the world responds to emerging health threats in future.”

This excitement over the early results, coupled with problems occurring in other vaccine trials, prompted officials to begin vaccinating people immediately. It is good news for people who are in close contact with infected individuals because the vaccine appears to provide some level of protection.

The problem is proving that the vaccine is responsible for people not getting sick. The step-randomization between the first two groups shows it may be providing protection, but there is nobody to compare against when everyone now gets the vaccine. That may present a problem when Merck, the drug company further developing the vaccine, tries to get approval to sell it, according to Wired magazine’s Katie M. Palmer.

“The early results out of Guinea were enough to convince the trial’s data safety and monitoring board to pull the emergency brake and start giving the vaccine to every person in the study. Now they’ll just have to hope that regulators agree,” she writes.

The U.S. Food and Drug Administration is paying attention. According to the Wall Street Journal, a commentary by the FDA was meant to be published alongside the research in the The Lancet. It critiqued the design of the study, indicating that the drug agency may not approve the vaccine if the current trial is used as evidence of its efficacy.

Despite the challenges, the trial is being hailed as a success for more than its results. A collaborative effort of health workers, researchers, regulators and governments allowed the vaccine to move quickly through the pipeline to allow the study. It took a lot of work to enact a public health intervention that involved tracking down cases and people connected to the infected individuals.

“That such a trial was even possible is a testament not only to the skill of the research teams but also to the commitment of communities to defeating an epidemic that has devastated their nation,” according to an editorial in The Lancet accompanying the research. “Over 90 percent of the study’s staff were from Guinea. Before this work, no clinical trial on this scale had ever been performed in the country.”

The strides made in implementing a medical trial during an outbreak may pave the way for future studies and rapid responses in the future.

“This is illustrating that it is feasible to develop vaccines much faster than we’ve been doing,” said Adrian Hill, director of the Jenner Institute at the University of Oxford, U.K., in an interview with Nature.


About Author

Tom Murphy

Tom Murphy is a New Hampshire-based reporter for Humanosphere. Before joining Humanosphere, Tom founded and edited the aid blog A View From the Cave. His work has appeared in Foreign Policy, the Huffington Post, the Guardian, GlobalPost and Christian Science Monitor. He tweets at @viewfromthecave. Contact him at tmurphy[at]