The mandatory quarantine orders announced Friday by the governors of New York and New Jersey were not very well-received. Aid groups like Doctors Without Borders and various medical experts spoke out against quarantining medical workers returning from Ebola-stricken West Africa because they fear such quarantines will make it harder to recruit people to go to West Africa in the first place. Some questions have also been raised about the legality of these quarantines.

There is also another problem with these quarantines: They won’t work. They will stop some people with Ebola from getting into the United States, but they cannot possibly stop every person with Ebola from getting into the United States. Quarantining aid workers will not stop more cases of Ebola from coming to the United States any more than checking the temperatures of travelers from Ebola-stricken countries could.

We do not live in a world where you can catch every instance of a virus that gestates for up to three weeks, could infect a person without their knowledge and cannot be detected for some or all of that infection period. We do, however, live in a world of porous borders and unpredictable events. Even if we do everything right and prepare for every possible eventuality, something will happen for which we did not or could not prepare.

Take the enhanced screening at U.S. airports, a measure announced more than a week after Thomas Duncan because the first person diagnosed with Ebola in the United States. (The first of only four confirmed cases so far, I might add, a fact that seems to be drowned out by the contagion of panic.) It is extremely unlikely that the enhanced screening, which involves temperature checks and detailed questionnaires, would have flagged Duncan during his trip from Liberia to Texas, because he had no fever when he traveled, and later said he had no idea he had the virus. Duncan, who died Oct. 8, also said he had not cared for a person with Ebola on a questionnaire he filled out at the Liberian airport. These measures could not possibly stop every case because they simply cannot account for every case.

The two nurses who contracted Ebola while caring for Duncan — the only two people to have contracted Ebola in the United States (so far) — also speak to the unpredictability of fighting a virus that needs specific conditions and narrow windows in which to infect people. They were health-care workers with training, operating in a medical facility that had protective equipment, and they still contracted the virus. They were not being monitored when they left work or, as we later learned, told not to travel on commercial airplanes.

People who treat patients with Ebola in the United States are not the people we typically think of when we talk about monitoring possible Ebola cases in this country. And New York Mayor Bill de Blasio commented on this when asked, a day after his city’s Ebola diagnosis, if the nurses caring for Craig Spencer in Manhattan were being monitored or isolated. “We need the best people, the most capable people, doing this work and we need to protect them, but they also do have the rest of their lives,” de Blasio said during a news conference last Friday. “So long as they’re taking those precautions, we can make that work.”

We still do not know how the nurses in Dallas were infected. We also do not know how Spencer, who worked for Doctors Without Borders in Guinea, contracted the illness. We may never know, as authorities have said. What we do know is that Ebola is known as a “caregivers disease,” as it generally afflicts those who take care of people with Ebola (or handle the bodies of Ebola victims).

Even if you look beyond our borders and focus on the nexus of Ebola on this planet — the epidemic that continues to be a living nightmare in West Africa, with more than 10,000 cases and more than 4,000 deaths so far — there is still no realistic way to keep the virus from making its way to the United States. Let’s say, for instance, that the U.S. airport screening measures work like a charm. And let’s say that every single person who would eventually develop the virus is otherwise found and identified, because they either have a fever during the screening or because they realize while answering the questionnaire that they exchanged bodily fluids with a person who had Ebola.

Yet every person who is screened is someone who started their trip in these three West African countries, which means the screening only goes so far. The monitoring programs outlined by the Centers for Disease Control and Prevention on Monday only cover people who know they had contact with an Ebola patient, which is not foolproof. A person could travel from Liberia to, say, London before unknowingly infecting another person; that person can board a flight to Los Angeles, unwittingly carrying a virus for which their travel history would provide no warning. A health-care worker treating an Ebola patient in New York could board a plane for Seattle to visit a loved one, unintentionally infecting a person on the other side of the country. These are hypotheticals, which means they are meaningless, but they speak to the fact that there are any number of eventualities that could lead to a person with Ebola in the United States.

Still, the current argument focusing on quarantines for returning health-care and aid workers ultimately focuses on an infinitesimal slice of the larger Ebola situation. During a news briefing Monday announcing the CDC’s new monitoring guidelines for people who have been to the Ebola-stricken countries, Thomas Frieden, the CDC director, mentioned that about 100 people people are arriving in the United States from this region each day. About five percent of these travelers are health-care workers. 

The only guaranteed way to keep anyone with Ebola out of the United States it to keep everyone from coming to the United States. That is unrealistic, of course, which is why the CDC and other public-health experts keep saying that the next-best option is to try and stop the outbreak in West Africa. These same experts do not think that quarantining five people a day will do much more than give other health-care workers another reason to think twice about heading to West Africa. These quarantines may make some people feel better, but they are unlikely to do more than that.