(CNN) -- President Barack Obama said Thursday that he opposes issuing a travel ban to stop Ebola from spreading from West Africa into the United States, explaining that "history shows that there is a likelihood of increased avoidance (that could lead to) more cases rather than less."
"The problem is that -- in all the discussions that I've had thus far with experts in the field, experts in infectious disease ... a travel ban is less effective than the measures that we are currently instituting," Obama said.
Asked whether he might appoint an Ebola czar, President Barack Obama said Thursday that "it may be appropriate for me to appoint an additional person" to focus exclusively on the virus.
Meanwhile, the Dallas hospital that's been ground zero for Ebola in the United States will soon officially be free of the virus after transferring the last of three infected patients that had been treated there, but not free of criticism or fallout.
Texas Health Presbyterian Hospital was where the first and, thus far, only three people diagnosed with Ebola in the United States have been treated. The first was Liberian national Thomas Eric Duncan, who died October 8. The next two were nurses who helped care for Duncan and contracted Ebola despite precautions intended to prevent just that.
One, Amber Vinson, was moved Wednesday evening to Atlanta's Emory University Hospital. It was her second flight this week, coming two days after she flew commercially from Cleveland to Dallas -- at a time when she was monitoring herself for Ebola and after, she said, someone at the CDC told her it was OK to fly despite having a slightly elevated temperature.
Texas Health Presbyterian Hospital nurse Nina Pham arrived via plane in Maryland on Thursday night. She was then transported, by ambulance, to the National Institutes of Health hospital in Bethesda, Maryland, just outside Washington.
The Dallas hospital said that transferring Nina Pham "is the right decision (because) many of the medical professionals who would normally staff the intensive care unit (are) sidelined for continuous monitoring." Some 76 workers who cared for Duncan, like Vinson and Pham, have been asked to do things like regularly take their temperatures to gauge whether they have Ebola.
Texas Health Presbyterian's critical care medicine chief Dr. Gary Weinstein said "she has improved so much in a short period of time." Pham sounded upbeat and grateful in the same statement about her upcoming move to Maryland.
"I'm doing really well thanks to this team, which is the best in the world," Pham said. "I believe in my talented co-workers."
Many of those co-workers are subject to heightened concern and scrutiny, due to their involvement in Duncan's care.
Still, the Ebola crisis in the United States is not confined to Texas Health Presbyterian Hospital.
On Thursday, it prompted the grounding of a Frontier flight crew and closures of schools in Texas and Ohio because people there flew on the same plane, if not necessarily the same flight, as Vinson.
And as has been common in recent days, flags have been raised about possible new cases nationwide -- such as that of a Yale University doctoral student who, having recently returned from Connecticut from Liberia, is in isolation and being tested for Ebola after coming down with a fever, Yale-New Haven Hospital officials said.
There also was a lot of Ebola-related activity in Washington. Some was proactive and far-reaching, such as President Barack Obama signing an executive order authorizing the deployment of National Guard troops to West Africa -- where most all of the nearly 9,000 reported Ebola cases and 4,500 deaths have been occurring, according to the World Health Organization -- to help authorities there deal with the devastating outbreak.
Closer to home, federal and Texas health officials faced heated questioning on Capitol Hill about how Ebola has been handled so far in the United States and how it will be handled in the future.
While procedures may change -- especially after some well-publicized mistakes -- Centers for Disease Control and Prevention Director Dr. Tom Frieden said his agency's overarching goal will not.
"Our top priority, our focus is to work 24/7 to protect Americans," Frieden said. "That's our mission."
Four now being treated in U.S. hospitals for Ebola
And it starts with saving the lives of those with Ebola now being treated in American hospitals.
One, freelance NBC cameraman Ashoka Mukpo, is "getting better every day" at Nebraska Medical Center, hospital spokesman Taylor Wilson said Thursday.
Emory University Hospital -- which previously treated Americans David Brantly and Nancy Writebol for Ebola -- was caring for an unnamed person with the disease who came there September 9.
Then there's Pham, the first person to contact Ebola in the United States (rather than get it in West Africa, then be flown to America for treatment).
As to Vinson, Dallas Mayor Mike Rawlings told CNN's Wolf Blitzer on Wednesday evening, "She's doing OK, but she was a little more progressed than Ms. Pham."
One positive sign is that Vinson was seen walking slowly out of an ambulance later that night into Emory's hospital.
The hospital that she left, Texas Health Presbyterian, remains very much on the defensive.
Dr. Daniel Varga -- the chief clinical officer for the hospital's parent company, Texas Health Resources -- admitted hospital staff "made mistakes" the first time that Duncan visited there in late September, letting him leave despite his symptoms and the fact he'd just come from West Africa.
"We did not correctly diagnose his symptoms as those of Ebola," Varga testified Thursday to the U.S. House Energy and Commerce Committee. "We are deeply sorry."
Schools closed, flight crew grounded
While these are the only people confirmed to have Ebola now in America, many more are on guard.
They include health care workers, such as Pham and Vinson, who were involved in Duncan's care. Many of them were asked to monitor themselves, but Vinson's flight from Cleveland-to-Dallas raised questions about the protocols for self-monitoring.
Frieden, the CDC director, has said that Vinson shouldn't have flown, especially with a temperature slightly above normal at 99.5 degrees Fahrenheit. At the same time, he acknowledged Thursday that "she did contact the CDC" about boarding the flight and claimed someone there cleared her to fly.
It's not clear who she spoke with at the CDC or what exactly she was told. Still, the fact such a conversation took place raised the possibility not everyone in the agency was on the same page.
It has also raised fears among the 132 passengers on Frontier Flight 1143 that they might have been exposed.
Frieden said there's an "extremely low" risk to anyone else on that plane, but the CDC is reaching out to all passengers as part of "extra margins of safety."
That didn't stop a few schools in Texas' Belton Independent School District from closing Thursday because two students were on the same flight. Two schools in the Solon school district in suburban Cleveland also shut down because a staffer "traveled home from Dallas on Frontier Airlines on Tuesday on a different flight, but perhaps the same aircraft" as Vinson, the school district said in a statement.
And Frontier Airlines removed the plane's seat covers and carpet near where the infected passenger sat, in addition to placing six crew members on paid leave for 21 days "out of an abundance of caution."
"We take today's events seriously as your safety and that of our customers is always at the forefront of everything we do," Frontier CEO David Siegel said.
They might not the only ones who won't be going anywhere anytime soon.
The federal government is weighing putting those who treated Duncan on a "Do Not Board list" that would prohibit them from flying commercially, an official familiar with the situation told Elizabeth Cohen, CNN's senior medical correspondent.
With two of its own nurses infected with Ebola, Texas Health Presbyterian Hospital "is offering a room" to any concerned employee "to avoid even the remote possibility of any potential exposure to family, friends and the broader public."
"We are doing this for our employees' peace of mind and comfort. This is not a medical recommendation," the hospital said. "We will make available to our employees who treated Mr. Duncan a room in a separate part of the hospital throughout their monitoring period."