Proposals to ban flights from Liberia, Guinea and Sierra Leone are not a surprising reaction to the Ebola crisis, but they have been rejected by those with expertise in the area and usually indicate a failure to consider the practicalities.

The idea to ban airplanes flying from West Africa has been advocated by senators, governors, and the Speaker of the US House, and has the support of 70% of Americans in a recent poll. However, many of these advocates don't seem aware that there are no direct flights from the three most affected countries to the United States, and none of the people pushing the ban seem to have a detailed plan for how it would work.

Consider citizens of wealthy countries currently in Liberia. Most would probably like to get home, if not now then soon. Which is more likely if flight bans are implemented: They simply accept they are stuck there until the crisis passes, or they make their way to a nearby country and fly on from there? Statistician Nate Silver has pointed out that the vast majority of flights from West Africa come from countries largely untouched by the crisis.

If any returnees have been infected with Ebola, they're going to bring it with them one way or another. But a ban will ensure they have spent a lot longer on airplanes and in airports, increasing the (still tiny) chance of infecting those around them, while running down their immune systems. Planes are great places to catch colds and flu, making it harder to identify who has ebola on arrival. They'll also be pretty pissed off, which may lead to not answering questions honestly. 

Meanwhile, the economies of the countries included in the ban will be badly damaged, hindering their capacity to bring the disease under control and probably triggering a mass exodus. A ban that stops aid workers traveling to West Africa would destroy any possibility of stopping Ebola's spread. On the other hand, what is the point of letting those who have been treating the sick come home, while banning people who were in the same country, but probably never came near an Ebola patient? All this in response to an estimated three infected people leaving the region per month. As Dr. Kamran Khan at St. Michael’s Hospital in Toronto said, “Decreasing the number of infections in the source area is the most important way to decrease the spread.” 

What about a ban on flights from the whole of Africa, even countries that are Ebola-free? Try explaining that to the millions of tourists in Morocco, South Africa and Egypt. Moreover, if one non-African country chooses not to go with this idea, everyone can make their way home through there.

An alternative version of the idea involves ignoring where someone is coming from, and banning anyone who has recently visited an affected country. This relies on accurate passport records, something the region isn't known for, and on the participation of all intervening countries – despite it being in those countries interests not to play ball.

The idea of trying to quarantine millions of people is unworkable, but particularly so for a disease like ebola. It takes up to 21 days (maybe more) for Ebola symptoms to appear, leaving plenty of time for people to hop around the planet, unlike influenza.  On the other hand, it is also quite unnecessary – Nigeria and Senegal had ebola outbreaks which have now been overcome. Anyone arguing that developed countries will soon see the disease spreading like wildfire is alleging their health systems are worse than countries with one-twentieth the average wealth.

People will, and always will, find ways to leave the country. Forcing them to use illegal, undocumented means is a sure-fire way to help ebola spread faster.