WS MoreOrLess: Ebola
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Hello and welcome to More or Less on the BBC World Service. I'm Ruth Alexander and if you've been listening to the news lately, you could be forgiven for feeling worried.
A big outbreak of the deadly Ebola virus in West Africa. The largest Ebola outbreak in history.
There is no treatment or vaccine.
Ebola is probably the most contagious and most deadly virus in the world. The strain can kill up to 90% of its victims. Most of those who get it will die through uncontrollable bleeding.
The outbreak of the lethal Ebola virus has spread in West Africa affecting Guinea, Liberia, Sierra Leone and Nigeria. As we heard there, this is the deadliest outbreak of the disease to date killing almost a thousand people so far. And as a deadly virus with graphic effects it seems the stuff of those dramatic Hollywood films about deadly viral pandemics. But before we panic, let's think. because more or less listener Max Cousins has been in touch with a question.
A widely reported statistic is that Ebola kills up to 90% of those infected. I've been wondering what this statement actually means. Is it that 90% die in some areas and less than 90% in others? If so, to what extent and why do mortality rates vary?
Yes, we've heard this statistic over and over again in news reports, but what does it actually signify? Well, more or less as James Fletcher has been finding out, and he's here to tell us.
Hi, Ruth. This figure of up to 90% comes from the World Health Organisation. It's a fairly simple measure called the case fatality rate. That's the number of people who die from an illness divided by the number of people who are diagnosed with that illness. Now, we asked Maimuna Majumda, she's a biostatistician and epidemiologist at MIT University in the United States, what the WHO mean when they talk about a fatality rate of up to 90%.
That 90% figure actually comes from one outbreak of Ebola, which took place in the Congo between 2002 and 2003. So it's the highest rate we've ever seen. We've also seen CFRs much lower than that in previous outbreaks. And I think that's something important to keep in mind. a CFR of 90% could be considered the upper limit of outbreaks caused by Zarebola virus. The cumulative average, considering all Ebola cases and deaths from 1976 to present, is actually closer to about 60 to 65%. And the current outbreak thus far has a CFR of about 54%, though it's subject to change as the outbreak wanes on.
Maimouna Majumda there said the current fatality rate is 54%. And as Max, our listener, was wondering, are all the countries with Ebola cases seeing that kind of rate?
No. So at the moment, the fatality rate varies a lot between the Western African countries that are affected. The worst affected country is Guinea, which was the first where the Ebola showed up. That's got a fatality rate of around 73%. whereas in Liberia it's lower at 55%, in Sierra Leone it's 41%, and in the most recently affected country, Nigeria, it's much smaller at 11%, although they've only seen a handful of cases there, so it's not really possible to draw firm conclusions about how deadly the outbreak there is or could be.
Those are big differences though.
Yes, Maimuna Majumde explains what can cause those variations in the fatality rates.
The two biggest factors that are influencing case fatality rate are, first, familiarity with the disease. This is the first time that we've seen Ebola in West Africa, so it caught everybody by surprise. And the second is availability of resources to contain, prevent, and treat the people that are sick. When you have large ranges in CFR, like you do with Ebola, it isn't really appropriate to give one extreme or the other. I think if we were to use CFR for Ebola, we really ought to give the cumulative average since the initial emergence of the disease in 1976. And that's significantly less than the 90% estimate that we hear a lot in the media and in news reports.
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