Ebola Is Back—and Vaccines Don’t Work Against It

Public health officials are racing to contain an outbreak in Uganda. It’s an urgent warning to the rest of the world.

The outbreak began on September 15. A 24-year-old man, suffering from a high fever and convulsions, was admitted to Mubende Regional Referral Hospital in Uganda. He had bleeding in his eyes and had been passing blood-stained vomit and diarrhea. The man died on September 19. The next day, laboratory tests confirmed the worst fears of those caring for him: Ebola was back.

And this outbreak is different. Ebola is a disease of multitudes. For the most common species of the virus, successful vaccines have already been developed. But for others, no vaccine exists. To the dismay of health officials in Uganda, the version of the virus found in the body at Mubende was from the Sudan species, for which there is no vaccine.

Other Ebola deaths have also been reported in the region. Six people from the man’s family, three adults and three children, also died between September 11 and 15. The Uganda Ministry of Health dispatched a rapid response team to the affected villages in Mubende district to do a verbal autopsy—collecting information on the likely cause of death from local people. The risk of infection from conducting a physical autopsy would be too high.

By October 16, the Ministry of Health had reported 60 confirmed cases of Ebola, having registered 11 new cases in the previous two weeks. In total, 24 deaths have been confirmed, including four among health workers, along with 24 recoveries. 

That as many people have died as have recovered is striking, but not surprising. Ebola is a rare but highly dangerous viral disease that kills roughly 50 percent of people who fall ill with it. Fruit bats are thought to be the natural host of the virus, but it can also infect primates, rodents, and humans, spreading via the bodily fluids of infected animals or people, both alive and dead.

Ebola has flared up intermittently in Africa for more than 40 years, most notably during an outbreak between 2013 and 2016 that infected 28,000 people and took more than 11,000 lives. During that outbreak, experimental vaccines against the most common form of the virus—the Zaire species—could be tested. They worked well, and have since been approved and used to protect people. But developing vaccines for rare viruses like Ebola is always a game of cat and mouse. The Sudan virus behind the current outbreak has caused only a handful of human cases over the past two decades. Work to develop vaccines to target this virus is underway, but none have been fully tested, let alone finished.

Using a Zaire vaccine against the Sudan virus isn’t an option, says Pontiano Kaleebu, director of the Uganda Virus Research Institute. “This has already been proven in the laboratory. The neutralizing antibodies do not respond,” he says. This means two things: that surveillance and physical control measures are currently the only tools available for limiting the virus’s spread, and that a working vaccine needs to be found as quickly as possible.

The candidate that’s farthest along is the single-dose ChAd3 Ebola Sudan vaccine, which is being developed by the Sabin Vaccine Institute, a nonprofit based in Washington, DC. By working with the World Health Organization (WHO), the Coalition for Epidemic Preparedness Innovations, and other organizations, the institute is planning to run a clinical trial in the current outbreak to see how well the vaccine works.

But there are only 100 doses available. With limited supply, health officials plan to give doses of the vaccine to immediate contacts of confirmed Ebola cases. Scientists then hope to use these contacts as potential candidates in the vaccine’s clinical trial—though the exact testing protocol they will use is still being worked out.

Kaleebu says they are hoping for accelerated production from the Sabin Vaccine Institute now that more doses are needed. But even if the number of vaccines used in the trial is small, they will still provide useful data, says Bruce Kirenga, a senior respiratory physician at Makerere University College of Health Sciences on the outskirts of Kampala.

“Trials use power calculation,” Kirenga says, referring to sums that allow researchers to work out the minimum number of people you need to involve to see whether a vaccine or medicine has an effect. A well-designed trial in an emergency situation in need of a drastic change of course—such as whether a vaccine stops someone from getting or dying from a severe disease like Ebola—doesn’t necessarily need to involve lots of people.

Doses of another candidate vaccine, designed to protect against both the Zaire and Sudan forms of the virus and developed by the University of Oxford, are also being sent to help in the outbreak. But the WHO has said that vaccine trials won’t start for another couple of weeks, meaning that for now, Ugandan authorities are relying on non-pharmaceutical interventions.

Contact tracing is being used to follow people who have been close to known cases, with more than 1,500 contacts having been traced as of October 16. Over a third of these are no longer being followed, having been traced for 21 days without developing symptoms.

New cases are also being picked up outside of the contacts being traced, says Daniel Kyabayinze, director of public health at Uganda’s Ministry of Health. “It’s a good sign of optimal surveillance,” he says. But it is also a sign that the limits of the outbreak are still uncertain.

On October 12, the Ministry of Health announced that a man had died of Ebola in a hospital in Kampala, having traveled to the capital from his local village. Three days later, two districts—Mubende and Kassanda—entered a three-week lockdown to try to stop the virus spreading. Bars, nightclubs, and places of worship have been closed, and only cargo trucks are allowed to enter or leave the districts.

With the risk of infection so high, trained teams are also being dispatched to bury the dead. And, at the same time, they are helping with the contact tracing—taking the details of all people the deceased could have had contact with. The Ministry of Health is also training health workers to handle Ebola cases, and communities are mobilizing volunteers and those who have previously worked in Ebola case management to take part in control efforts.

Neighboring countries have also stepped up their vigilance. Common border points between Uganda, Rwanda, and the Democratic Republic of the Congo are both surveilling the virus and isolating known contacts. In Uganda, border health control teams are managing any emergency cases of Ebola among travelers. It’s a challenge. “The tests we have don’t work for the two viruses,” says Otim Patrick Ramadan, health emergency officer at the WHO Regional Office for Africa. Two monoclonal antibody treatments—which enlist the immune system to fight against diseases—recommended for treating the Zaire virus also don’t work against the Sudan virus, he says.

Despite the hard task Uganda faces, the WHO has expressed optimism about its ability to tackle the outbreak. “Thanks to its expertise, action has been taken quickly to detect the virus, and we can bank on this knowledge to halt the spread of infections,” Matshidiso Moeti, the WHO regional director for Africa, said on October 6. “Uganda is no stranger to effective Ebola control.”

If Covid-19 was a big reminder of the threat of emerging infectious diseases, then Ebola is a quieter but equally dire warning. To a degree, the world got lucky with the pandemic: If something as transmissible as SARS-CoV-2 and as deadly as Ebola emerged in the future, the resulting outbreak would change the course of history.

To prepare for the worst case scenario, lessons must be learned from this outbreak—and where it came from. Ebola and Covid-19 are both diseases that jumped to humans because humanity continues to encroach on wild areas of the planet. “People are going to look for food, or they are mining, or it’s leisure activities,” says Otim. “As the frequency in interaction between humans and animals increases, we pick up these viruses from them.”

Updated 10-18-2022 11:00 am ET: The discussion around the number of cases, fatalities, and recoveries in the current outbreak was updated for clarity, with a calculation of the case fatality rate in the current outbreak (previously corrected) being removed. 

Ebola Is Back—and Vaccines Don’t Work Against It

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