The two nurses who contracted Ebola from Thomas Duncan, the first Ebola patient diagnosed in the US, have set off a national panic over how easily the virus can be caught. But a deeper look at Duncan's case shows just the opposite: how incredibly hard it is to catch Ebola. (Here's how you can, and can't, catch the disease.)

This past Sunday marked 21 days — the full incubation period for the infection — since health officials began following Duncan's close contacts. Today marks a full month since he took several flights from Monrovia to arrive in Dallas on September 20.



None of the people on Duncan's flight have fallen ill. Nor did Duncan's fiance, or his family — whom he lived with while he was running a sweaty fever and vomiting.

Duncan's fiance is virus-free

Amid the panic and fear about Ebola sweeping the US, let's be clear about one fact: as far as we know, two nurses who cared for Duncan got the virus — but no one else. Not the passengers who sat next to Duncan on his flights or touched the same surfaces as him in airports. Not the school kids and friends he met in Dallas. Not the Texas Presbyterian hospital staff who met him on his first visit, when he was misdiagnosed and sent home. Not the ambulance drivers who brought him to the hospital on his second visit, when he was vomiting with a high fever.



Most importantly, his fiance, Louise Troh, didn't catch the virus either. She shared a cramped apartment with him and several other family members while he was already contagious, and then stayed in the same contaminated space, cooped up for days in a quarantine, after Duncan was admitted to hospital.



So far, all these people have been declared virus free. And the dozens of suspected cases of Ebola across the US have turned out to be negative, except for three — Duncan and his two nurses, Amber Vinson and Nina Pham. The fact that they got sick while caring for Duncan should also remind us of the science of this virus: that fits what we know of the science of the virus, which is that people are most contagious late in the infection.

This is really important: part of what makes people so afraid of Ebola is that people infected with the disease can mistake it, in its early stages, for a normal flu, and, say, board a plane. But at that point, the disease just isn't very contagious yet.



Vinson and Pham came into contact with Duncan when the disease had taken over his body — and without the full personal protective gear that we know now they should have had access to.

The virus is behaving as scientists expected

This tells us that the virus is behaving just as public-health officials expected it would. It infected Duncan, and when he was shedding the maximal amount of virus just before his death, it infected two of his caregivers. The reproductive rate for the Ebola virus — the number of infections that one sick person creates — is about 1.5 to 2, reflecting the Ebola situation here.



The good news that Duncan didn't infect more people in America comes alongside good news from Nigeria: the country has just been declared Ebola-free after registering no new cases for 41 days.



There, health officials aggressively followed all the contacts of "patient zero" — and the contacts of those who got Ebola from him — until they recorded no new cases.



Dr. Margaret Chan, the World Health Organization Director-General, said the Nigerian report shows that Ebola is containable when action is taken early. "If a country like Nigeria, hampered by serious security problems, can do this — that is, make significant progress towards interrupting polio transmission, eradicate guinea-worm disease and contain Ebola, all at the same time — any country in the world experiencing an imported case can hold onward transmission to just a handful of cases." Even with the a regretful series of fumblings, it appears America has so far succeeded, too.

Dallas should be a wake-up call for hospitals



Unfortunately, we are not yet in the clear. There is still time for another health worker who cared for Duncan to test positive, or for one of the contacts of the Ebola-positive nurses to get sick.



As well, it's only a matter of time before more Ebola cases turn up outside of the three countries — Sierra Leone, Guinea, and Liberia — that have been crippled by the virus.



So the Texas situation should be a reminder of two things: first, health is truly global and viruses don't respect borders. While there are only three Ebola cases here, there are more than 8,000 in West Africa. As long as the Ebola outbreak is raging over there, no country is safe. Resources need to be invested in helping West Africa overcome Ebola, and not on irrational, fear-based policies, such as travel bans.



