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Estimating how many people need treatment during an Ebola outbreak

21 Aug, 2014

Ebola virus virionToday the Wellcome Trust has announced a multi-million pound funding package to support research during the current Ebola epidemic in West Africa. There’s no sign of an end to the outbreak and many people believe things will get worse before they get better, so it’s important to understand the scale of the challenge we face. Oliver Brady is an epidemiologist from the University of Oxford, who has been working in this area with colleagues Professor Simon Hay and Dr Peter Horby. Here, he explains why this outbreak requires special attention…

Last week a World Health Organisation (WHO) Expert Committee reached the conclusion that it would be ethical to consider unproven drugs during this exceptional Ebola outbreak in West Africa.

This ground-breaking decision raises some immediate questions: what investigational drugs and vaccines are available, and what volume of each would be required in the current epidemic?

Rapid answers to these questions are necessary in order to plan the development of any of the candidate drugs or vaccines, for this, and future outbreaks.

Prof Simon Hay, Dr Peter Horby and I have spent some time looking at how we might come up with some figures to provide a useful starting point for discussions. It is important to note that it is not our intention to provide exact figures, but rather to enable us to judge the potential need in an epidemic of this scale, compared to previous outbreaks.

To reach these estimates we extracted a range of published data from 22 previous outbreaks of Ebola spanning back to 1976. This data includes contact-tracing studies and staffing needs during the outbreaks, which allowed us to approximate the number of people that may have been exposed to the Ebola virus per infected person or per bed.

We created four different categories to reflect the different groups potentially exposed to Ebola virus. These categories are: Ebola patients and their close contacts, healthcare providers and those who dispose of the bodies and infectious material, other essential service providers including logistics personnel and a contingency stockpile for controlling infections that spread outside West Africa.

By estimating the numbers of people in each of these categories who might be exposed to infectious individuals, we were able to work out how many people could have been eligible for treatment or vaccination over the course of the outbreak so far.

While the people in these different categories may be at very different levels of risk for developing the disease, until we have a better understanding exactly what constitutes a significant contact we have to assume that all of these individuals may require treatment or prophylaxis.

Our results show that, under a conservative scenario, up to 30,000 people may have been eligible for treatment or vaccination between the start of the current epidemic in December 2013 and 19th August 2014.

This scenario is considered conservative as it is based on data from past Ebola epidemics in isolated rural communities. The difference in scale of the current urban outbreak means that many of these historical parameters may be underestimates.

It is clear that the magnitude of need for the current on-going epidemic is already significantly higher than any previous Ebola outbreaks. Furthermore we are seeing no signs of the epidemic easing and action is urgently required given the considerable gap between need and the tools we currently have available.

The next step is for those involved in manufacturing or commissioning potential therapies to refine our initial estimates, taking into account the specific therapeutic or preventive characteristics of each drug or vaccine. The financing and roll-out of investigational drugs will also have an effect on the number of treatments required, but we hope that the groundwork that we have put in will assist in this process.

Mathematical models of the epidemic will also be important in refining the numbers and helping to determine the optimum intervention scenarios when the effectiveness and modes of action of the candidates are known.

The scale of the current Ebola outbreak in West Africa means that we have no time to waste. Now is the time for decisions to be made on financing, scaling up production and evaluating investigational and novel Ebola therapeutics.

Our preliminary estimates of the number of people that might have been eligible for treatment or vaccination since the start of this outbreak, if the products were available, gives us an a better idea of the scale of the challenge we face.

We hope that our tool will facilitate prompt, evidence-based decisions on the scale of financing and manufacturing required for these potential therapeutics and vaccines.

Made now, these decisions may have the capacity to mitigate the mortality and improve the control of the current Ebola outbreak, as well as those that may occur in the future.

You can read Oliver Brady’s article on Nature.com in their ‘World View’ section and find the spreadsheet they used for calculating the number here. Oliver Brady (BBSRC funded) and Prof Simon Hay (Wellcome Trust funded) are in the Spatial Ecology and Epidemiology Group, University of Oxford, and Dr Peter Horby is from the Epidemic Diseases Research Group, Centre for Tropical Medicine and Global Health, also at the University of Oxford.

The Wellcome Trust has announced new funding to support research that could take place during the current Ebola outbreak and in future epidemics. More information can be found in the news section of the Wellcome Trust website.

Image credits: Ebola virus – CDC/Cynthia Goldsmith/Public Health Image Library, Vaccination – Barbara Bellingham, Wellcome Images

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