Pressure is mounting for governments to ban the entry of travellers from Liberia, Sierra Leone and Guinea, where the Ebola epidemic is growing exponentially with 5000-10,000 new cases per week expected by December, up from fewer than a thousand now.
They have a point. Calculations published this week show that at least three people carrying Ebola are likely to fly from the affected countries each month, two-thirds of them to poor countries with limited healthcare, where they could set off further outbreaks.
Despite this, health and development experts are unanimous that a ban on outward air travel would be disastrous. Privately, UN officials warn that such a move could lead to a panicked rush of people across land borders, where unlike air passengers their movements cannot be traced. It could also cause further economic damage to the countries, threatening the civil order essential to fighting the disease.
A dozen African countries have closed their borders to people from the affected countries, but other borders are open. The US, UK and Canada are screening arrivals for fever. Last week US President Barack Obama said he would not rule out further limitations. Many airlines have already cancelled flights, meaning that there has been a reduction of between 50 and 85 per cent in the number of airline seats available from the three countries.
Even with those reductions, Kamran Khan at the University of Toronto in Canada and his colleagues report that on average, 2.8 people per month who are already infected with Ebola will fly from the three countries internationally – and that number will rise as case numbers grow. The team recommends improvements in the existing system: screening passengers for exposure history or fever before departure.
The problem is that Ebola incubates, without causing fever, for an average of nine days and as many as 21. Two-thirds of infected people, says the European Centre for Disease Prevention and Control (ECDC) in Copenhagen, would be symptom-free at departure, and if asked about potential exposure, could either hide it or be unaware.
So far exit screening hasn’t worked terribly well. Of 36,000 travellers in the first two months of exit screening, says the ECDC, 77 were stopped, most because they were running a fever. None turned out to have Ebola. One infected, pre-symptomatic Liberian man, Thomas Eric Duncan, got through the system, however, and reached the US.
The same problem limits the effectiveness of screening passengers on arrival. Entry screening failed to stop any cases of SARS moving in 2003.
So if neither exit nor entry screening works, why not simply stop anyone leaving the countries while we get the epidemic under control?
The first reason is that travel bans are unlikely to be very effective. Steep reductions in flights after the 9/11 bombings only delayed the subsequent flu season, and closing borders to the HIV-positive in the 1980s did not slow the HIV pandemic.
In both cases, that was because people carrying the infection still managed to get through, and that is likely now. “It’s simply not feasible to build a wall – virtual or real – around a city or a country,” Tom Frieden, head of the US Centres for Disease Control and Prevention in Atlanta, Georgia, said last week. People stopped from flying out of the three affected countries will find other ways to travel.
Moreover, a travel ban would further reduce commercial flights to the region. This could discourage badly needed foreign healthcare workers from volunteering, as with no military airlift planned, they need commercial flights to get home.
Finally, a flight ban could make the epidemic much worse, by hastening economic and social collapse in the affected countries, says Thomas Homer-Dixon of the University of Waterloo, Canada, who studies social resilience.
This would be catastrophic, preventing any further organised effort to fight the infection. Moreover, a collapse in food distribution or public safety could send a flood of refugees across land borders, carrying Ebola to nearby, impoverished countries.
Those most affected by a flight ban are what sociologists call “elites” – expatriates and locals who run major employers and infrastructure such as food processing plants, mines, plantations, banks and power plants. Various expatriate populations in the region are linchpins of commerce and the crucial mining industry, for example. Flight bans could cripple their operations; mining is already suffering.
As the epidemic worsens, Homer-Dixon says, these people will leave before a ban kicks in. “Provision of food, water and electricity could start to collapse, and international health workers would be forced to leave.”
That point could be hastened by the threat of a closed border. Elites have always fled plagues, says Peter Turchin of the University of Connecticut in Storrs, even in the Black Death of 1348. That means the classes that travel by air will strongly resist any limitation on their mobility.
The answer, he says, is an invention born of the Black Death. “You don’t stop flights from West Africa. You simply require travellers to spend the necessary time in quarantine before they are allowed to move on”. This way, anyone incubating the virus will become known – and can be isolated.
But there are no plans to do this because it would delay all passengers by weeks, to catch an infection known to have reached only 0.05 per cent of the population.
A modern equivalent could be testing travellers for the virus. Several companies are developing rapid tests using a pinprick of blood to reveal infection even during incubation. The World Health Organization is in turn developing a procedure for assessing which ones work well enough to solve the travel problem – but nothing will be available before next year.
Journal reference: The Lancet, DOI: 10.1016/S0140-6736(14)61828-6
Leader: “Cutting off the Ebola zone would be a mistake“
More on these topics: