Ebola won't spread to many people in the United States unless the virus mutates, a top federal health official told Congress on Thursday as fallout continued from the infection of a second Dallas nurse who had treated a now-dead Ebola patient and then flew on a commercial airline.
"There is zero doubt in my mind unless there's a mutation there will not be a large-scale outbreak in the U.S.," said Dr. Thomas Frieden, director of the federal Centers for Disease Control.
Frieden's comments came as both he and the Obama administration resisted renewed calls for a travel ban for three West African countries that are currently dealing with the worst Ebola outbreak since the virus was discovered in the mid-1970s.
Hours later, the CDC said it will now track passengers who were on a plane with Ebola-infected nurse Amber Joy Vinson took from Dallas to Ohio last Friday, in addition to the passengers it was already tracking from a flight she took back to Dallas on Monday.
"We can't rule out that she might have had the start of her illness on Friday," Dr. Chris Braden of the CDC said at a briefing, as he cited new information developed by investigators tracing all of Vinson's contacts. Vinson would have become contagious after developing symptoms.
Read MoreOfficials spar on Ebola travel ban
The U.S. Health and Human Services Department on Thursday said it is providing $5.8 million in funding to accelerate development of a third Ebola vaccine, by Profectus BioSciences Inc. Two other potential vaccines, one produced by GlaxoSmithKline, the other by Canada's public health agency and NewLink Genetics, are currently undergoing clinical trials.
"We are pushing hard to advance the development of multiple products as quickly as possible for clinical evaluation and future use in preventing or treating this terrible disease," said Robin Robinson, director of HHS's Biomedical Advanced Research and Development Authority.
There is no vaccine currently approved for Ebola, nor are there any approved treatments for the virus. However, at least three experimental drugs have been used on an emergency basis for several Ebola patients during the current outbreak, although it is not clear if the drugs worked.
Obama announced Thursday that he had authorized the use of American military reservists for humanitarian aid against the Ebola outbreak in West Africa. He did not indicated how many people would be required for the mission.
So far, three people have been diagnosed with Ebola in the U.S.: Liberian national Thomas Eric Duncan, who flew to Dallas in mid-September from Liberia, and two nurses who treated him after he was admitted to Texas Health Presbyterian Hospital in late September. Duncan died there on Oct. 8.
One of those nurses, Vinson, may have had symptoms of the virus days she flew on a commercial airliner with 132 other passengers on Monday from Cleveland to Dallas, officials said Thursday.
That revelation led Frontier Airlines to put six crew members on paid leave out of an "abundance of caution," the airline said.
It was also revealed Thursday that 13 nurses from Ohio were on an earlier flight with Vinson when she flew on the same airline last Friday to Cleveland from Dallas. The other nurses, from the Cleveland Clinic and MetroHealth Medical Center, are all now on paid leave.
Ebola patients are contagious if they are showing symptoms of the virus, which is transmitted through contact with bodily fluids. However, officials have noted repeatedly that the virus is not easily transmitted.
Seven people in the Akron, Ohio, area are in voluntary quarantine, and one business there, a bridal shop, has voluntarily closed temporarily because Vinson visited the area, officials said. The 29-year-old traveled to Ohio, where she has family, to prepare for her upcoming wedding.
People who visited the Coming Attractions bridal shop in Akron between the hours of noon and 3:30 p.m. Eastern Time on Saturday have been asked to call the Summit County [Ohio] Public Health Ebola Hotline, an operator who answered that number confirmed.
A school in Akron was closed Thursday and is being cleaned after officials learned that the parent of a child there had spent time with Vinson during her trip. The mother is now in quarantine, as is the child, despite the fact that the child had not had contact with Vinson, officials said. The Akron school will remain closed until Monday.
A middle school and an elementary school in Solon, Ohio, closed Thursday after officials learned that a staff member at those schools may have traveled on the same plane—but not the same flight—as Vinson on Tuesday, officials said.
The CDC had already asked passengers who were aboard the same flight with Vinson on Monday to contact the agency for possible monitoring for the virus. CDC officials said Vinson only began showing a fever on Tuesday morning, and was isolated in Texas Health Presbyterian Hospital within 90 minutes of reporting her condition.
But later Thursday, the CDC said it now wants to track passengers from both Monday's flight, and last Friday's.
Frontier Airlines CEO David Siegel, in an email to airline employees, said that Frontier was later "notified by CDC that the passenger [Vinson] may have been symptomatic earlier than initially suspected; including the possibility of possessing symptoms while onboard the flight."
Siegel said that because of that disclosure, the airline is keeping the plane out of service, and is flying it back to Cleveland from Denver without customers.
Vinson and Nina Pham, another nurse at Texas Health Presbyterian, became sick in the past week from Ebola after having cared for Duncan, who died in the hospital on Oct. 8 from the virus. It is not known exactly how they became infected.
Vinson was flown on Wednesday from Dallas to Atlanta, where she is being treated at Emory University Hospital, the same facility that is currently treating another Ebola patient, and which previously treated two Americans who have since recovered from the disease.
Pham, 26, is expected to be transported from Dallas to the National Institutes of Health's isolation unit in Maryland, officials said. That move could happen later Thursday.Dr. Tony Fauci, the nation's top infectious disease expert, will personally weigh in on nurse Pham's treatment at the NIH's special containment unit.
"I am going to go see her tonight when she arrives," Fauci told reporters after the Congressional hearing on the Ebola response.
Pham, in a prepared statement released by the hospital, said, "I'm so thankful or the outpouring of love and support from friends and family, my coworkers and complete strangers. I feel very blessed, and have gained strength from their support. I appreciate everything that my coworkers have done to care for me at Texas Health Presbyterian Hospital Dallas. I'm doing really well thanks to this team, which is the best in the world. I believe in my talented coworkers. I am #presbyproud!"
Dallas County Judge Clay Jenkins said Pham's transfer will leave available all three isolation units at Texas Health Presbyterian for use if there are future Ebola patients.
Vinson's mother, who has been in Dallas since Oct. 14, is in voluntary quarantine in Dallas, a county official said. She has no symptoms but is being monitored.
Even before Vinson's diagnosis, more than 120 people were being monitored for signs of Ebola. They include 48 of whom had contact or may have had contact with Duncan before his admission to the hospital, and about 75 health-care workers other than Vinson and Pham who treated him or handled his blood afterward. None of the people being monitored has shown signs of Ebola.
The hospital Wednesday night said that it was offering a room to any of the workers who were being monitored "who would like to stay here 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."
The Texas hospital has been under scathing criticism for initially not having admitted Duncan for treatment when he first appeared there on Sept. 25, and for allegedly having insufficient protocols to protect health-care workers in dealing with him once he was admitted three days later.
Brianne Aguirre, a friend and co-worker of Pham's, told NBC's "Today" show on Thursday that she and more than 100 other workers there were not given special instructions for dealing with potential Ebola patients and that Duncan initially was put into an area at the hospital with "up to seven other patients."
Aguirre described confusion over procedures for dealing with Duncan, including how to handle his lab work, and a failure to discuss Ebola as an issue for concern prior to his arrival.
"I watched them violate basic principles of nursing," Aguirre said. "I would try anything and everything to refuse to go there to be treated. I would feel at risk by going there."
Texas Health Presbyterian, in a statement, said, "Our hospital followed the Centers for Disease Control guidelines and sought additional guidance and clarity" while treating Duncan.
Later Thursday, in testimony to Congress, the chief clinical officer and senior executive vice president of the hospital's operator, Texas Health Resources, said, "It's hard for me to put into words how we felt when our patient, Thomas Eric Duncan, lost his struggle with Ebola on Oct. 8."
"Unfortunately, in our initial treatment of Mr. Duncan, despite our best intentions and a highly skilled medical team, we made mistakes," said Dr. Daniel Varga of Texas Health Resources. "We did not correctly diagnose his symptoms as those of Ebola. And we are deeply sorry."
Varga also said that emergency staff at the hospital were not trained this summer on how to handle the virus, despite warnings from health officials about the outbreak in West Africa.
Duncan's fiancée, Louise Troh, in a statement released Thursday said that earlier the same day, "I received a phone call from an executive with Texas Health Resources Presbyterian Hospital. The purpose of this call was to apologize to me for the death of my [fiancé], Thomas Eric Duncan, and to express regret that the hospital was not able to save his life. This official said the hospital was 'deeply sorry' for the way this tragedy played out."
"I am grateful to the hospital for this personal call. I am grateful to God that this leader reached out and took responsibility for the hospital's actions. Hearing this information will help me as I mourn Eric's death," Troh said.
In Madrid, Spain's health ministry said it was investigating a possible case of Ebola aboard an Air France flight.
Dallas County commissioners tabled a vote Thursday on the question of declaring a local state of disaster because of Ebola.
In Sierra Leone, one of three West African countries that are at the center of the current Ebola outbreak, the last district in the country that had remained untouched by the virus reported two Ebola cases, officials said. There were 425 new cases reported in Sierra Leone in the past week.
The World Health Organization said Thursday the worldwide death toll will soon pass 4,500 people, including 236 health workers.
International health officials warned earlier this week that Ebola could end up infecting 10,000 people per week by December in West Africa at its current rate of progression, unless efforts to contain the disease are ramped up.
"It will take months before this outbreak is stopped," Dr. Isabelle Nuttall, a director at the World Health Organization told reporters in Geneva.
House of Representatives Speaker John Boehner, R-Ohio, said President Barack Obama should a travel ban from countries afflicted by Ebola. So far, the Obama administration has resisted calls for a travel ban, saying it would hurt efforts by medical workers to contain the disease in the affected countries, which they say is the best way to prevent further cases in the U.S. and Europe.
The White House said Thursday that it is still against instituting a travel ban on West African countries suffering from Ebola outbreaks.
However, four airports on Thursday were set to join New York's JFK Airport in taking the temperatures of passengers from Sierra Leone, Liberia and Guinea to screen them for Ebola. The airports are in Washington, Chicago, Atlanta and Newark, New Jersey.
In his testimony before Congress, CDC Director Frieden dodged travel ban questions, but eventually said, "We will consider any options to better protect Americans," when pressed by Rep. Timothy Murphy.
Obama on Thursday was briefed by his cabinet about the response so far. Obama later said, "the dangers of a serious outbreak in this country are extraordinarily low, but we are taking this very seriously."
U.S. Sen. John Cornyn, R-Texas, called on Obama Thursday to appoint someone to coordinate the response to Ebola nationwide. Cornyn was previously briefed by Texas Health Commissioner Dr. David Lakey and other officials from Dallas.
"The situation in Dallas has quickly gone from one of concern in North Texas to one that all Americans are now rightfully worried about," Cornyn said.
"The White House has done little over the past few weeks to inspire the confidence of Texans and the time for the administration to act is now. The president should immediately designate an experienced, proven leader to coordinate a national response involving local, state and federal agencies to contain Ebola in the United States, including considering temporary restrictions on travel from impacted West African nations."
A survey released Thursday found that a large number of Americans, 45 percent, are worried they or a family member will contract Ebola.
The Kaiser Family Foundation survey also found that 73 percent of Americans believe that it's more likely that the virus will be contained to just a small number of cases in the U.S. Just 22 percent told Kaiser pollsters that a widespread outbreak is more likely.
And 73 percent of the public said that if there were an Ebola case near where they lived, they would have a "great deal" or "fair amount" of confidence that the CDC would be able to contain the outbreak and prevent it from spreading, according to the KFF survey, which questioned 1,503 adults.
The survey was conduced from Oct. 8 through Tuesday, which covers the time that Duncan died and Pham tested positive for the virus. It does not include the period when Vinson's diagnosis with Ebola became public.
CORRECTION: It was revealed on Thursday that 13 nurses from Ohio were on a Frontier Airlines flight with an Ebola-infected nurse. An earlier version of this story misstated the date.
—Reuters contributed to this report