Medical attendants with red bag outside the Ebola isolation section of Mubende Regional Referral Hospital, in Mubende, Uganda.

Health-care workers walk outside an Ebola isolation unit at a hospital in Mubende, Uganda, on 29 September.Credit: Hajarah Nalwadda/AP/Shutterstock

In the past month, at least 64 people in Uganda have been — or are suspected of having beeen — infected with a rare species of the Ebola virus, for which no vaccines or treatments are available. About 30 people have died. The rapid rise and spread of the lethal virus across five districts in Uganda have alarmed scientists, and raised fears that the outbreak will not be easy to contain.

“It’s definitely concerning,” says Daniel Bausch, director of emerging threats and global health security at FIND, the global alliance for diagnostics in Geneva, Switzerland. “The slope of that curve is pretty sharp.”

Ebola is a rare and deadly disease — with a death rate that has ranged from 25% to 90% in past outbreaks. The first symptoms to develop are usually fever, vomiting, headaches and fatigue, but the condition can worsen quickly to include damage to internal organs and death.

Two main viral species give rise to Ebola in humans: Zaire ebolavirus and Sudan ebolavirus. Zaire ebolavirus caused a large epidemic from 2013 to 2016 in West Africa that spurred the development of vaccines and treatments, which have since transformed the fight against Ebola. But similar therapies for Sudan ebolavirus — responsible for the current outbreak in Uganda — are still in clinical trials. The most recent outbreak caused by this species occurred in 2012 in Uganda.

The situation is serious, says Fiona Braka, an emergency-response programme manager at the World Health Organization Regional Office for Africa in Brazzaville, Republic of the Congo. “But Ebola is not new to Uganda,” she says. Five previous Ebola outbreaks have taken place in the country, four of which were caused by the Sudan species. An outbreak in 2000 — the largest in Uganda so far — involved 425 infections and 224 deaths. So the country is familiar with the rapid-response measures needed to contain the virus, Braka says.

Although Sudan ebolavirus had not been known to cause a human infection in about a decade, it was only a matter of time before it resurfaced, says Kartik Chandran, a virologist at the Albert Einstein College of Medicine in New York City. “These viruses are out there,” he says, “and we don’t have a good handle of where they hang out in nature, and how they transmit to people.” Ebola outbreaks have been difficult to prevent, because animals such as some monkeys and bats can carry the viruses and spread them to people. In rare cases, the viruses can linger silently in a person’s body for months or even years after an initial infection1, only to emerge later and spread to others.

Vaccines are not enough

Because Sudan ebolavirus outbreaks have been rare, researchers have not been able to test vaccine candidates thoroughly. Three vaccines have undergone early tests to ensure that they are safe in humans, but the larger trials needed to confirm efficacy haven’t been possible.

There are currently six candidates in the pipeline. The one that is furthest along is a single-dose vaccine that was developed in part by the US National Institute of Allergy and Infectious Diseases (NIAID) in Bethesda, Maryland, and is licensed to the Sabin Vaccine Institute in Washington DC. A study has shown that this jab is protective against the Sudan species in non-human primates2. One hundred doses might be shipped from NIAID to Uganda as early as next week, says Richard Koup, the acting director of NIAID’s Vaccine Research Center.

These should be prioritized for hospital workers, including health-care personnel who are interacting with people who have been infected and their direct contacts, and the contacts of those contacts, says Gary Kobinger, a virologist at the University of Texas Medical Branch in Galveston who specializes in Ebola. Still, vaccines and antivirals, even if proved to be effective, will not stop the outbreak just because they exist, Kobinger says. To achieve that, enough doses need to be produced quickly and then distributed widely, which will pose a challenge, he adds.

The good news is that clinical trials for these experimental vaccines and treatments are being organized at a breakneck pace, Kobinger says. Researchers hope to start trials later this month, which is in stark contrast to the more than eight months that it took before trials began during the large West African epidemic, he adds.

This is important, because health officials are in a race against time. The farther the virus spreads geographically, the more stretched the already-sparse resources will become, Kobinger says. And some are concerned that the virus could easily find new footholds: the outbreak encompasses regions in Uganda that contain gold mines that attract many people, as well as a busy road that leads to the neighbouring Democratic Republic of the Congo, Braka says.

Fortunately, health officials in Uganda are putting lessons from previous outbreaks into practice. For example, using a mobile laboratory in Mubende, the outbreak’s epicentre, health-care personnel can detect the virus in a sample within six hours, Braka says — rather than having to send all the samples to the Uganda Virus Research Institute in Entebbe.

Braka urges countries bordering Uganda to have Ebola test kits ready to distribute, and to ramp up surveillance for the virus. Countries outside Africa are also on alert. The US Centers for Disease Control and Prevention announced on 6 October that the United States will redirect travellers coming from Uganda to one of five US airports that are able to screen for the virus.

Right now, the outbreak is at a make-or-break moment, Kobinger says. He hopes that containment measures will stop the spread, but he fears that it could “really get out of hand”.