Congo’s Ebola epidemic reached 5,713 confirmed cases and 2,744 deaths on August 25. Nearly half of everyone confirmed infected has died. It has reached six provinces and 58 of the country’s 151 health zones, and it is the largest in Congo’s history.
Congo declared it in May. By that time, the virus had already been circulating for months. Counting from the declaration measures how long officials have been monitoring, not how long transmission has been going on. Those missing months are much of why it reached this size, but only part of the explanation. The other is that transmission hasn’t yet been brought under control.
Measured the same way, the West African epidemic of 2014 had 779 cases at this point, and Congo’s North Kivu epidemic of 2018, which killed 2,299 people over nearly two years, had 295. Congo’s count has doubled every 2.2 weeks, against 5.3 weeks in West Africa, and that gap compounds. West Africa went on to infect 28,652 people, the worst filovirus outbreak on record, and it still needed 26 weeks to reach the total Congo has hit in 15.
Ebola Spreads Slowly Enough To Stop
Bundibugyo virus is a relatively poor transmitter. Analysis by researchers at the London School of Hygiene and Tropical Medicine estimated the reproduction number early in this outbreak to be about 1.9, so on average each patient infected roughly two others, and two weeks separate one generation from the next. Patients become contagious only once they are visibly, severely ill.
That combination is what makes Ebola controllable. Responders have time to reach a patient’s contacts before they show symptoms, and people who are infectious can be identified quickly. For comparison, Covid spread at a serial interval near five days through people who felt well, which is why tracing failed against it. Ebola outbreaks before West Africa were stopped by finding contacts and watching them for 21 days, without a vaccine.
In June, epidemiologists at the CDC simulated the outbreak under different isolation rates. If 70 percent of patients reached isolation, one simulation in 20 exceeded 10,000 cases within three months. At 20 percent, 65 percent of simulations exceeded 20,000.
Congolese teams reached 84.6 percent of listed contacts on August 25, a high figure in a conflict zone.
No Vaccine Works Against This Strain
Ervebo, which helped end the North Kivu epidemic, protects against Zaire ebolavirus. This outbreak is Bundibugyo, a different species. WHO’s vaccine advisers have declined to recommend Ervebo outside research settings, and the licensed antibody treatments Inmazeb and Ebanga are Zaire specific too.
The Coalition for Epidemic Preparedness Innovations is funding four studies on cross protection, none of which is expected to report during this outbreak. So that means beds, patient care, tracing and isolation are the entire response.
The Isolation Wards Filled Up
Writing in Nature Medicine, Justin Kambale Kahingi and two colleagues in Kinshasa and Butembo report that in early August Ebola treatment centers were beyond full, which was further fueling the epidemic. When a ward fills, they wrote, infection control degrades inside it and suspected cases wait at home, both of which accelerate transmission. In Congo’s August 2 situation report they found the Nizi treatment center, in Ituri, at 278 percent of capacity.
The national picture is better than that suggests. Ituri, where approximately 83 percent of cases have occurred, was at 57 percent occupancy that day and is below 50 now, after capacity grew from about 690 beds in mid-July to 978. A major part of the challenge has been how dispersed this outbreak has become.
Another indicator to monitor is the impact on health workers. WHO counted 151 such infections by July 30, of whom 44 died, and Julien Harneis, the United Nations Ebola coordinator in Bunia, increased the count to 160 three weeks later. Those patients fared far better than the public: 29 percent died, against 48 percent overall. Partly, that is because they are recognized early and receive prompt care.
The Case Count Is Falling For The Wrong Reason
Of the 57 cases confirmed on August 25, eleven were already dead when found. Each marks some point in a chain of transmission that ran invisibly and may not yet have terminated.
On the other hand, daily counts have drifted down through late August, from about 109 a day in late July to roughly 70 in the final week. That is not yet compelling evidence the epidemic is turning. Deaths held near 40 a day while cases fell, and the case fatality ratio rose slightly from 45.6 to 48 percent. Epidemics in retreat do not usually grow more lethal, while surveillance missing milder infections produces exactly this pattern.
The London School model estimates that the outbreak response drove that reproduction number down to slightly greater than 1 by mid July. That is a real achievement and not enough. The reproduction number has now hovered around 1 for about six weeks. An epidemic held at 1 does not shrink. For containment to be achieved in a reasonable time frame, the response must reduce the current rate of transmission by roughly half, but that seems unlikely. Even then, the outbreak will stretch well into next year.
The London School model also estimates the level of under-reporting, suggesting that there have been between 8,600 and 10,300 infections compared to the 5,713 that have been identified. Indeed, the true tally is likely even larger.
It is not too late to stop this outbreak, however. Uganda has been a notable success, recording 20 cases from the same epidemic early on but ending it quickly, as declared today by the Africa CDC and WHO after 42 days without a new case. It faced the same virus without a vaccine and stopped it in under three months.
Congo’s epidemic is still the kind of problem beds, staff and tracing can solve. West Africa was smaller than this at a hundred days, and it did not stay that way.
