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How Effective Is Airport Screening Against Ebola?

It's at least not totally worthless, according to a new study.
Image: David Prasad/Flickr

Airport screenings for Ebola aren't completely worthless. This is the finding of a new study published in the journal The Lancet. Using a mathematical model, researchers at the University of Liverpool were able to calculate the probability that the virus will make it into either the United States or the UK given the total number of infected individuals likely to fly before the end of the year. Of 29 Ebola carriers attempting to leave West Africa by airplane, 10 will be symptomatic and detectable.

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It's easy to be cynical about airport Ebola screenings. For one thing, we already have a really good head-start, with attitudes toward post-9/11 security expansions tending more towards scorn than relief (at least anecdotally). Taking a deplaning passenger's temperature may just seem like more theater, yet a crucial difference is that instead of the audience being fellow air travelers, it's an anxious populace at large: subway riders, restaurant diners, etc. People that spend money.

Meanwhile, it's perfectly possible to transport Ebola through an airport checkpoint undetected, which is clear even without the support of some mathematical demonstration. Ebola has an asymptomatic incubation period of around a week, a period in which the traveler will not have an elevated temperature.

So, we're left with passengers traveling with symptoms, a dwindling subset given the decreased likelihood of someone with Ebola symptoms jumping on a plane in the very first place. It's possible, but certainly less likely than the symptomatic case.

Of those 19 asymptomatic cases likely to leave West Africa, only one or two will attempt to enter the UK with up to three attempting to enter the US, according to the model. Given that Ebola has so far only been exported on two occasions by air travelers, those numbers seem about right.

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Even with the limited effectiveness of air traveler screening, the Liverpool team seems firmly in favor of continued efforts. Indeed, while some recent epidemic models suggest that it only takes one or two infected individuals to maintain the exponential growth of an outbreak, those tend not to take into account containment and control measures (such as those already in place). One or two Ebola sparks making it into the US or the UK isn't likely to set an Ebola fire.

"In addition to identification of those individuals infected, entry screening allows health authorities to provide information to passengers arriving from west Africa, describes actions to take if they become unwell, and helps with follow-up," the current study notes. "Although entry screening could reduce the overall chances of Ebola being brought into a country, the most effective way to restrict its global spread is to control the disease at source in west Africa."