Merck's Ebola vaccine, in short supply, is given only to people at high risk of infection. 

REUTERS/James Akena

As Ebola outbreak rages, plan to test second vaccine sparks debate

When the Democratic Republic of the Congo (DRC) declared its 10th Ebola outbreak in August 2018, it had one weapon that was unavailable during the previous nine: a highly effective vaccine, produced by Merck & Co. Ten months later, health workers have administered some 130,000 doses, yet the epidemic is still raging; it is now the second largest in history, with more than 1500 deaths.

That’s why experts will gather in Kinshasa on 28 June to discuss a thorny issue: whether, and how, to deploy a second vaccine to supplement the limited supplies of the Merck shot. Fielding it would also provide a rare opportunity to test another vaccine’s effectiveness. But some experts worry a new effort could drain resources from the primary vaccination campaign and complicate efforts to persuade people to get vaccinated. “Having two vaccines ... raises an important potential for confusion and skepticism,” says political scientist Rachel Sweet at the University of Notre Dame in South Bend, Indiana.

DRC Minister of Public Health Oly Ilunga Kalenga told Reuters last month that he preferred to stick with one vaccine, so as not to “perturb the population.” The DRC convened this week’s meeting to help him and other officials “make an informed decision,” a government spokesperson says.

The Merck vaccine has performed well during this outbreak and in a formal clinical trial in Guinea. It consists of a live but harmless vesicular stomatitis virus engineered to carry a gene for an Ebola surface protein. A single dose rapidly leads to immunity; the vaccine is “probably one of the major factors that have kept this a smoldering outbreak rather than an explosive one,” says Daniel Bausch, who leads the United Kingdom’s Public Health Rapid Support Team in London.

But there’s not much of it. The World Health Organization (WHO) in Geneva, Switzerland, says some 250,000 doses of the vaccine are still in stock, but Natalie Roberts of Doctors Without Borders in Goma, DRC, says not everyone who is eligible gets the vaccine because too little of it is arriving. To stretch supplies, the vaccine is only used in contacts of known Ebola cases and in contacts’ contacts, as well as in nurses, doctors, and others whose jobs may expose them to the virus.

But at the moment, only 60% or so of the contacts can be traced, in part because of the deep distrust of the government and international organizations in the war-torn region hit by Ebola. As a result, says Jeremy Farrar, head of the Wellcome Trust in London, the Merck vaccine “will keep a lid on the epidemic, but will not bring it to an end.”

A WHO advisory group has repeatedly recommended offering additional vaccines to lower-risk populations in the DRC. After reviewing two candidates, it recommended a vaccine made by Johnson & Johnson that requires two shots: one of a nonreplicating adenovirus that includes an Ebola surface protein, and then, 8 weeks later, a modified pox virus with several Ebola proteins that also does not replicate. The hope is that the combination will give long-lasting protection.

Doses for 1.5 million people are now available, and scientists at the London School of Hygiene & Tropical Medicine have produced a protocol for deploying them. They suggest offering shots to anyone more than 1 year old. To help establish the vaccine’s efficacy, scientists would later test anyone seeking treatment for certain Ebola-like symptoms and see whether a smaller percentage of those who actually have Ebola were vaccinated, compared with those whose symptoms are a false alarm.

The fact that the new vaccine would be given to entire communities makes it attractive to local leaders, Sweet says. The current, selective approach opens the door for favoritism in who gets access to the vaccine, Abbé Telesphor Muhindo Malonga, president of the civil society in Butembo, DRC, recently wrote in a WhatsApp message to his followers.

But where the vaccine would be used is up for discussion. In one scenario it would be given to lower-risk people in communities that have already seen infections; in another it would go to communities that have not yet had Ebola cases, such as Goma, a city of 1 million and the capital of North Kivu, the province at the center of the DRC outbreak. Sweet says, “There is some wisdom” in first targeting places where the virus hasn’t yet hit and rumors aren’t rife; it would be difficult to explain why people in the same village receive different vaccines. But Roberts says it’s more important to immunize people in the affected areas.

A consortium including WHO and the Coalition for Epidemic Preparedness Innovations—an Oslo-based public-private partnership to develop vaccines against neglected diseases—is ready to implement the study of the Johnson & Johnson vaccine. “Essentially, it is pending authorization from within DRC,” Farrar says.

Others worry that fielding a second vaccine could strain existing efforts. Some also ask how many people will return for their booster vaccination. Bausch says one option is to offer a deworming treatment or some other incentive to bring people back to the clinic. “This has to responsibly address a real problem,” and can’t be “some hollow gesture,” he says. But even one shot should offer some immunity, Bausch adds.

He hopes this week’s meeting will convince doubters that the second vaccine deserves a trial. The Ebola community should be “looking at how we stop this outbreak,” he says, “but also making sure we have the tools to stop future ones.”