It’s been 21 days and none of the people in closest contact with Thomas Eric Duncan in the days before he was hospitalized has gotten sick. That includes his fiancée Louise Troh and her children, who were in a small Dallas apartment with an increasingly ill Duncan for days, and forcibly kept inside for days afterward.

No one else has carried Ebola into the country yet, and since Wednesday, no more nurses or other health care workers who took care of Duncan have been infected.

What has been seen is what the Centers for Disease Control and Prevention and other experts predicted would happen — that someone might carry Ebola into the United States, and that they might even infect a few other people. What CDC has always promised is that it would stop there.

“I for one, am quite encouraged by the fact that 21 days have elapsed and Thomas Duncan’s family have not become ill,” said Jennifer Nuzzo, a senior associate at the University of Pittsburgh Medical School’s Center for Health Security. “It’s further evidence of what public health specialists have been saying: that this virus is not easily transmitted.”

Nurses Amber Vinson and Nina Pham had “extraordinary contact” with Duncan and, as in Liberia, Sierra Leone and Guinea, they were at the highest risk. People who lived with Duncan, rode in vehicles with him and spoke with him did not catch Ebola.

“It’s starting to show us the science we talked about at the very beginning is working,” said Dallas mayor Mike Rawlings.

Yet schools have closed, teachers and students who might have been in contact with someone who was in contact with a patient have been asked to stay home. Public schools in Moore, Oklahoma, have said they will ask students and an administrator to stay home because they were on a cruise ship with an uninfected — and now cleared — lab worker who handled Duncan’s blood. Doctors say the chance that any of those students could be infected is zero.

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Members of Congress continue to demand travel bans even though every expert who knows about such measures has said they not only don’t work, but they could make matters worse. People who have merely traveled to Liberia are asked to stay away from speaking engagements.

Vigilance Where It's Needed

The past three weeks have illustrated just how difficult it is to be vigilant about an infectious disease without swerving into overkill. If Texas Health Presbyterian Hospital had been thinking Ebola, Duncan would have been isolated and treated on Sept. 25 and wouldn’t have been so ill when he did start getting treatment.

It’s impossible to say that he may have lived, but experience shows that prompt treatment does raise the survival rate. And now the CDC is planning to issue new, clearer guidelines about what gear nurses and other health care workers should wear to protect themselves.

“I wouldn’t be surprised if the new guidelines today were more streamlined,” Nuzzo said.

And while the CDC’s been lambasted for not having been more forceful with hospitals, former Health and Human Services Secretary Mike Leavitt points out that local officials and even individual hospitals were also supposed to have been on the ball. “States and local governments, not just in Dallas, not just in Nebraska, not just in Bethesda, have got to be prepared for this," Leavitt said on MSNBC’s Daily Rundown.

“As it spreads across Africa the likelihood of it returning to the United States is high and we need to be ready for that.”

A Beer Can In Snake's Clothing?

More than 9,000 people have been infected in West Africa and while half have been confirmed to have died, the World Health Organization says the numbers are certainly higher. The epidemic is not even close to being under control and aid organizations say the help they’ve been screaming for is slow to arrive.

As long as the epidemic rages, people are likely to carry the virus elsewhere. That doesn’t mean the system has failed, Nuzzo says. “People are on high alert. So finding a case here and there in a hospital is not a case of the system failing but of the system working,” she said.

It may also mean more school closures.

“It’s unfortunate but understandable because people are acting on their emotions,” she said. “If shutting down a school to clean it means people will feel safer going the next day, then it is worth doing.”

Dallas County Judge Clay Jenkins has a folksy way of explaining such reactions.

"I've seen and heard of horses spooked by a snake and go running and that's probably a really good idea if you’re a horse,” he told a news conference Monday.

“I’ve seen and heard of horses spooked by a beer can. And beer cans don't usually attack horses often. So there's not much reason for running from a beer can. This is more of a beer can at this point than a snake.”

However, calls for travels bans will also pick up. And if another case appears, it may be more difficult to say no to such calls, says Dr. Peter Hotez, an infectious diseases expert at the Baylor College of Medicine.

“That is something we have to actively fight against,” Nuzzo said. “It may make people feel better but it won’t make them any safer.”