A figure in the new CDC paper shows that delaying intensified control measures will lead to vastly more new cases later. (For the full paper, click here.)

A figure in the new CDC paper shows that delaying intensified control measures will lead to vastly more new cases later. (For the full paper, click here.)

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WHO, CDC publish grim new Ebola projections

Six months after the World Health Organization (WHO) was notified of the Ebola outbreak in West Africa, its experts have released a new study warning that the situation is quickly growing worse and that Ebola may even "become endemic among the human population of West Africa, a prospect that has never previously been contemplated.”

The U.S. Centers for Disease Control and Prevention (CDC) in Atlanta, meanwhile, released a new model for the spread of the deadly virus. Its worst-case scenario estimates that up to 1.4 million people could be infected by the end of January. If control efforts are stepped up in a truly dramatic fashion and prove a stunning success, however, the epidemic could be almost over by that time. "Delay is extremely costly in terms of lives and efforts,” CDC Director Tom Frieden said at a press conference today.

The Ebola outbreak, which probably started in Guinea in December last year, has already sickened at least 5843 people, according to the latest WHO figures—more than twice as many as all known previous outbreaks combined—and killed 2803. Epidemiologists expect the real numbers to be two or three times that, however, because only a fraction of cases is reported. And the spread of the disease keeps accelerating.

The new study by WHO experts and scientists at Imperial College London, published today by The New England Journal of Medicine, is "excellent" because it fills some important gaps, says Preben Aavitsland, a Norwegian epidemiologist. “For instance, the study gives an average length of hospital stay of 6.4 days,” he says. That is important to know, because it means that about as many beds are needed as there are new Ebola cases every week. It also means that tens of thousands of beds will be needed by the end of November, Aavitsland says. “It’s completely unclear where those beds and the people to staff them will come from.”

The authors have also estimated the so-called reproductive rate of the virus in each country, which represents the average number of people that each infected person in turn infects. It ranges from 1.38 in Sierra Leone to 1.51 in Liberia to 1.81 in Guinea. That means cases are roughly doubling every 2 weeks in Guinea, every 3 weeks in Liberia, and every month in Sierra Leone, says Christl Donnelly, an epidemiologist at Imperial College London and one of the study's authors. “The big thing is that we are still seeing exponential growth and that needs to be stopped.”

A month ago, in its so-called Ebola Response Roadmap, WHO wrote that the number of cases “could exceed 20,000 over the course of this emergency.” In the new model, it projects that number to be reached by 2 November, if the epidemic continues to grow unchecked.

There is more bad news. Although WHO has earlier said that roughly half of the Ebola patients die, the paper estimates that the case fatality rate is actually just above 70%. “I think that that can be brought down through more aggressive therapy to well below 50%,” Aavitsland says. Offering a better shot at survival is important to convince patients to seek care instead of staying home, he says, where they may infect others. “At the moment, all these treatment units have to offer is a lonely death.”

In a perspective published with the article, Jeremy Farrar, head of the Wellcome Trust, and Peter Piot, director of the London School of Hygiene & Tropical Medicine, warn that knock-on effects will kill many more people. "West Africa will see much more suffering and many more deaths during childbirth and from malaria, tuberculosis, HIV–AIDS, enteric and respiratory illnesses, diabetes, cancer, cardiovascular disease, and mental health during and after the Ebola epidemic,” they write. "Indeed, there is a very real danger of a complete breakdown in civic society, as desperate communities understandably lose faith in the established systems.”

The model released by CDC today looks further ahead, and its projections are even more sobering. If the virus continues to spread at the current rate, Liberia and Sierra Leone alone will have reported about 550,000 Ebola cases by 20 January, the authors write. But if the official numbers so far represent only 40% of the real burden—which many believe may well be the case—that would mean a total of 1.4 million Ebola cases in those two countries by 20 January. “I certainly hope that we see nothing like those projections,” Donnelly says. “But I think it is a realistic projection of what would happen if we didn’t get our act together.”

Projecting what happens in Guinea is impossible because of the wild swings in case numbers there, Frieden said. “You see three separate waves of cases which have increased in amplitude” that probably reflect reimportations from the other two countries, he said at the press conference.

CDC has also released the model as an Excel spreadsheet “so that planners in countries as well as international organizations can model what might happen in different circumstances,” Frieden said. He also said that he doesn't believe the most dire predictions will come to pass. "The model shows, and I don’t think this has been shown by other modeling tools out there, that a surge now can break the back of the epidemic,” he said. Specifically, the epidemic begins to slow down, and will eventually peter out, if approximately 70% of the patients are in medical care facilities or Ebola treatment units, or—if those are all full—are cared for in such a way that they don't transmit the virus to others.

Although that may sound somewhat reassuring, it is unclear how this can be achieved, because doctors may not even know about 60% of all Ebola cases in the region. "I just don’t see the massive surge in help that is needed to achieve that,” says Jonas Schmidt-Chanasit, a virologist at the Bernhard Nocht Institute for Tropical Medicine in Hamburg, Germany. Partly, Schmidt-Chanasit says, it is a question of speed. The United States, for instance, has pledged 17 field hospitals that will be able to accommodate 100 patients each—but it's expected to take 50 to 100 days for those to be fully functional. By that time, the need will be much bigger already.

The CDC model shows this need for speed very clearly: For every 30 extra days it takes to get 70% of patients into treatment, the researchers estimate that the number of daily cases occurring at the peak of the epidemic will triple. Providing home care kits to protect people who take care of family members themselves may help prevent at least some infections, Schmidt-Chanasit says. “It is definitely a good idea, but it will not by itself curb this epidemic.” The key, Aavitsland says, is still a massive scaling up of beds and staff. “It seems very hard to stop this now, but I think we all just have to believe that it is possible.”

There is at least a glimmer of hope in the new data, Donnelly says. “The reproductive rate, at least in Sierra Leone and Liberia, was higher at the beginning of the epidemic. That may be a first sign that some of the efforts are having an effect,” she says. Christian Althaus, an epidemiologist at the University of Bern, cautions that this may just be an artifact, however. As hospitals have filled up, the share of cases going unreported may have increased, creating the illusion of some improvement. “I wish it were true,” Althaus says. “But I doubt it.”

*The Ebola Files: Given the current Ebola outbreak, unprecedented in terms of number of people killed and rapid geographic spread, Science and Science Translational Medicine have made a collection of research and news articles on the viral disease freely available to researchers and the general public.

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A 3D plot from a model of the Ebola risk faced at different West African regions over time.
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