How worried should you be about Ebola?

What is Ebola, how is it transmitted and when was it first discovered? How dangerous is it to those who are infected?

Ebola is a severe viral illness caused by viruses called orthoebolaviruses, which circulate in fruit bats in central and west Africa. It takes its name from a river in what’s now the Democratic Republic of Congo (DRC), near where it was first recognised in 1976.

Within that group, four cause disease in humans: Zaire, Sudan, Bundibugyo, and Taï Forest. The Zaire virus has been responsible for the largest outbreaks we’ve had to date, including the 2014–2016 epidemic in West Africa and 2018–2020 epidemic in DRC. The Sudan virus has driven several outbreaks around South Sudan, Uganda, and the DRC. Taï Forest is very rare; there’s only one known human case, in Côte d’Ivoire in 1994.

Ebola spreads through direct contact with an infected person’s bodily fluids, blood or vomit, or surfaces those fluids have contaminated. How dangerous it is depends on the strain and on whether patients can get to good supportive care. The Zaire virus, thought to be the deadliest, kills up to 90 percent of those it infects when untreated. The Bundibugyo strain behind the current outbreak has historically killed 25 to 40 percent.

Those are still terrifying numbers. But death rates drop sharply with intensive supportive care, the kind that keeps patients hydrated and their blood pressure and oxygen stable. During the 2014 West Africa outbreak, mortality ran 40 to 70 percent across affected countries; for the small number of patients evacuated to Europe and the U.S., it was closer to 20 percent.

What is the size of the current outbreak and where is that outbreak happening?

The first thing worth saying about this outbreak is that it’s already the third largest Ebola outbreak ever recorded.

And it started that way, which is the worrying part. For an outbreak to be that big the moment we notice it means the virus had been spreading quietly for some time before anyone recognised what was happening.

It’s centred in northeastern DRC, with confirmed cases in three provinces: Ituri, Nord-Kivu, and Sud-Kivu. As of the latest figures, there are around 750 suspected cases and close to 200 suspected deaths inside DRC. Across the border in Uganda, five cases have been confirmed, with one death. All of those Ugandan cases have clear travel links to DRC, which suggests local transmission hasn’t started inside Uganda yet. The reported case count is almost certainly an undercount. Colleagues at Imperial College London recently published work suggesting the outbreak could be as much as double its reported size and suggest we’re meaningfully under-detecting cases, and that wider transmission than we can see right now is probably happening.

How does it compare to previous outbreaks, especially the 2014 outbreak?

What worries me about this outbreak is the combination of where it’s happening and what we don’t have to fight it with.

The 2014–2016 outbreak in West Africa was the largest in history, and it changed Ebola response. It drove the development of vaccines and monoclonal antibody treatments for the Zaire variant of the virus that have since become transformative. By the time of the 2018–2020 outbreak in eastern DRC, those tools were available, and ring vaccination (see below for more details about this type of vaccination effort) became central to bringing it under control.

Even so, that outbreak infected nearly 3,500 people and killed over 2,000. I was working in Goma, DRC, with WHO during the response, and even with the tools, it was very challenging. Armed groups attacked treatment centres and health workers. Displaced populations moved constantly across porous borders.

In the current outbreak, we don’t have that toolkit. The vaccines and monoclonals are specific to the Zaire virus and likely won’t work (or work as well) against Bundibugyo. We’re effectively back to where we were before 2014, relying on supportive care and the older public health measures: case isolation, contact tracing, safe burials, community engagement.

And the setting is, if anything, worse than it was in 2018. The same provinces in eastern DRC, the same insecurity and displaced populations, with several more years of conflict on top. Less foreign aid going in. A weaker WHO presence after the U.S. withdrawal. It’s not yet as large as the 2014 or 2018–2020 outbreaks. But it’s already the third largest on record, and the trajectory worries me. There’s real potential for it to become one of the deadliest Ebola outbreaks we’ve seen to date.

How have previous outbreaks ended? Have they ended spontaneously or through vaccine development or through public health measures like isolation, etc?

Outbreaks end by breaking the chains of transmission.

In practice that means finding cases fast, isolating them in specialised Ebola treatment units, tracing every contact those patients had, monitoring them for 21 days, and burying the dead safely, because Ebola is particularly transmissible from the recently dead. You keep doing that until you’ve gone 42 days without a new case. That’s the core toolkit and it hasn’t changed a great deal since Ebola was identified in 1976.

Since 2014, for the Zaire strain, we’ve added ring vaccination, an approach borrowed from smallpox eradication. You vaccinate the contacts of confirmed cases and the contacts of those contacts, creating a protective ring the virus can’t easily cross. This was a huge reason we were able to successfully turn the tide on the 2018–2020 outbreak in DRC. This approach, and its associated success, is contingent on community trust. If people don’t believe what responders are telling them, if they don’t want their loved ones taken away by strangers in PPE, or receive the vaccine, the whole response collapses. We saw a crowd set fire to hospital tents near Bunia last week after being told a body wouldn’t be released for burial. Community sensitisation has to be the foundation of any response. The technical interventions build on top of it.

How worried should Americans be about this strain of Ebola making its way to the United States?

Of course, people hearing this news are worried, and understandably so. Let me try to be clear about the actual risk.

WHO’s global risk assessment remains low, and that’s grounded in biology, not reassurance. Ebola isn’t transmissible the way SARS-CoV-2 is. It doesn’t spread through the air. It needs close contact with the bodily fluids of someone who is already sick. And it doesn’t start transmitting until people are visibly unwell, which makes finding and isolating cases relatively straightforward.

Compare that to a virus like COVID, which spreads freely before people even know they are ill. So even if sporadic cases linked to travel from the region show up in the U.S.—and that’s unlikely—there’s a defined playbook: Identify, isolate, trace contacts, treat.

We saw it work in 2014 when there were a handful of imported cases (often in returning healthcare workers) and which were managed successfully in the U.S. that year without wider spread.

The bigger picture is that this is a horrible situation in eastern DRC and across the border in Uganda. The people I’m most worried for are the ones actually living through it. The healthcare workers in Bunia. The families of patients in Goma. If a case reaches the U.S., the patient will receive world-class supportive care and the chain will be cut. That’s not something people in eastern DRC can rely on right now.

Are the travel restrictions currently in place going to be effective enough at preventing spread through travelers? Do you anticipate the restrictions growing tighter?

Significantly expanding the monitoring of incoming travellers and ensuring they’re adequately tracked and traced, particularly if the epidemiology suggests they might be at high risk (due to where they have travelled recently), is useful. I’m less certain about complete travel bans.

Entry screening can pick up cases (or potential cases) at the border, particularly because Ebola doesn’t transmit until people are visibly unwell. Combined with the 21-day post-arrival monitoring of travelers from affected countries, that’s a real layer of defence. But the limits are also real. Ebola’s incubation period runs 2 to 21 days, so someone exposed in DRC can pass through screening healthy and develop symptoms weeks later. Follow up has to be airtight.

Complete travel bans are a little bit more complex. While they might have some scope to initially limit importations, they’re a very blunt tool, and the version we have now is both broader than the epidemiology warrants and risks compromising the response.

The current restrictions cover travelers from all of DRC, Uganda, and South Sudan. Treating Kinshasa, on the opposite side of the country from the outbreak, the same as Bunia, which is at its centre, isn’t epidemiologically sound. This is why WHO has long opposed broad national travel bans.They push people toward informal crossings, where there’s no screening at all. They can choke off responders and supplies going in the other direction.

And history tells the same story repeatedly. During H1N1 (the swine flu pandemic in 2009), the virus had moved internationally before bans were in place. COVID bans delayed spread by days or weeks but never prevented it. With mpox, heavy border focus pulled attention from the testing, surveillance, vaccination, and community work that actually controlled the outbreak.

Will restrictions tighten? Probably, particularly if any case is detected in the U.S., even one with no onward transmission. But tighter isn’t the same as better. If the goal is actually preventing introductions, the answer is serious support for the response on the ground to support containment of the epidemic at its source.

Is there anything else you think readers should know about the disease or the global situation as it stands now?

With the current situation on the ground, the risk is fraught for people there. People in eastern DRC are facing a deadly virus in conditions that make every part of the response harder. Hospitals are overstretched, and instability, conflict, and extreme poverty make day-to-day life immensely difficult and movement dangerous.

Communities there don’t have access to supportive care, a vaccine, or anything else that might shield them from this virus and its potentially deadly impact. And right now, exceptionally brave healthcare workers and public health responders are putting themselves in real danger to contain it, to protect these people, and us.

They are trying to stop an outbreak from becoming something much worse, for the region and for the rest of the world. All these people need our help, including funding, supplies, accelerated vaccine development for Bundibugyo, and political support for the global health institutions that coordinate this work.