How widespread is natural Ebola immunity?


The devastation that the world’s worst Ebola outbreak is wreaking in West Africa is both heart-rending and alarming. Expert projections suggest worse is yet to come, and with cases now confirmed in the US and Europe, there are rising concerns that outbreaks may occur on other continents. However, as the virus continues to infect and kill thousands, it may also be silently immunizing an unknown number of others.

As the latest figures from the World Health Organization (WHO) show, there are nearly 9,000 cases of Ebola in seven countries: Guinea, Liberia, Nigeria, Senegal, Sierra Leone, Spain and United States, and nearly 4,500 deaths. The disease has also taken its toll on healthcare workers, with 427 infected and 236 dead.

Experts predict that the Ebola situation in West Africa is going to get much worse without a large-scale, prompt global response, as fragile local health systems collapse under the strain of the disease.

A few weeks ago, using a new prediction model, the US Centers for Disease Control and Prevention (CDC) estimated that by early 2015, the number of Ebola cases could exceed half a million or more if effective prevention and control measures were not implemented promptly. The model suggested the number of cases was doubling every 20-40 days.

At a recent news conference in Geneva, Dr. Isabelle Nuttall, WHO Director for Global Capacities, Alert and Response, said their data shows “cases are doubling every four weeks,” and the disease is “still widespread in Guinea, Liberia and Sierra Leone.”
Ebola projections do not account for effect of immune people

But according to a letter in The Lancet medical journal, there may large numbers of people in West Africa – as yet unidentified – who are coming into contact with Ebola but never fall ill or infect others, and who may also be protected from future infection.

And if the effect such immunity can be confirmed, say the authors, it could have a significant impact on projections of how widely Ebola will spread. It could also help contain the outbreak.

They urge public health authorities to carry out a prompt investigation to establish how commonplace such immunity to Ebola might be. How many people have been infected without developing symptoms or spreading the disease? And are they likely to be protected from future outbreaks?

Co-author Dr. Steve Bellan, a postdoctoral researcher in the Department of Integrative Biology at The University of Texas at Austin, says:

“Ultimately, knowing whether a large segment of the population in the afflicted regions are immune to Ebola could save lives.”

Immune individuals could save lives by helping with disease control

If such individuals can be reliably identified, they could be recruited to help with disease control, reducing risk of infection to those who are not immune.

“We might not have to wait until we have a vaccine to use immune individuals to reduce the spread of disease,” urges Dr. Bellan. He and his co-authors also note that:

“Recruitment of such individuals might be preferable to enlistment of survivors of symptomatic Ebola disease because survivors might experience psychological trauma or stigmatisation and be fewer in number – in view of the asymptomatic proportions suggested in previous studies and the low survival rate of symptomatic cases.”

The authors say there is evidence from previous Ebola outbreaks that some exposed people do not develop symptoms, but it is not clear whether it is because they have developed immunity to the virus.

They conclude that finding out whether naturally immune people exist could make a big difference to efforts to contain Ebola, and could also affect the accuracy of projections.

The investigation needs to be as soon as possible, not only in order for any findings to have the chance to make a difference and save lives in the current outbreak, but because you can only be sure of finding individuals that are immune during an outbreak, as the authors explain:

” … the extent of protective immunity after asymptomatic infection and the identification of serological markers for protective immunity can only be definitively addressed in settings with ongoing transmission risk.”
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