Story highlights Two airports in London to implement enhanced screenings

Screenings begin Saturday at New York airport; four more begin next week

Emergency rooms in the United States are preparing for possible cases

World Health Organization: 8,399 are believed to have caught the virus; 4,033 are dead

Health screenings to help prevent the spread of Ebola began Saturday for some travelers to New York's John F. Kennedy International Airport but an official with the Centers for Disease Control and Prevention warned that nothing can "get the risk to zero."

Four other airports will add the screenings Thursday, according to the CDC.

This won't be a mass event, with long lines of travelers waiting for screening. Only about 150 travelers a day will receive the screenings, CDC officials said.

"No matter how many of these procedures are put into place, we can't get the risk to zero," Dr. Martin Cetron, director of the CDC's Division of Global Migration and Quarantine, told reporters Saturday.

"That will not be the case but this additional layer should add a measure of security to the American public. This entry screening procedure, for example, would not necessarily have caught the patient in Dallas."

Cetron was referring to the only case of Ebola so far diagnosed on U.S. soil -- that of Thomas Eric Duncan, who didn't have symptoms at the time he arrived in the United States.

Under the program, passengers originating from Guinea, Liberia, and Sierra Leone will be subject to the additional screening.

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Coast Guard corpsmen and eventually medical workers under contract will take the passengers' temperature and Customs and Border Protection staffers will ask questions about their health and possible exposure to Ebola.

Those suspected of possible Ebola exposure will be referred to a CDC public health officer for additional screening.

After the initial run Saturday at JFK, the testing will expand Thursday to Washington-Dulles, Newark, Chicago's O'Hare International Airport and Hartsfield-Jackson International Airport in Atlanta.

The five airports, JFK included, receive 94% of air travelers who come from the afflicted countries, according to the CDC.

"The expanded screening measures provide this layer of protection to the already established protocols to minimize the risk of another case of Ebola here in the United States," said R. Gil Kerlikowske, commissioner of U.S. Customs and Border Protection.

Kerlikowske said travelers with fever or other symptoms or who may have been exposed to Ebola will be referred to the CDC to determine whether they can travel or should be taken to a hospital. In addition, Border Patrol agents will monitor travelers for signs of illness.

Cetron said all travelers leaving the affected countries are already being screened with questionnaires about possible exposure and symptoms and having their temperatures checked.

"More than 36,000 passengers have been screened with this tool the last two months and not a single Ebola case has been detected," he said.

Will it help?

Some critics of the U.S. approach say the screenings won't do much from a public health perspective.

"I think they offer some margin of, I don't know, peace of mind for the public," said Laurie Garrett, a senior fellow for global health at the Council on Foreign Relations and author of "The Coming Plague."

But she stressed the screenings would not have detected Duncan's case.

"So I see this more as something to calm the nerves of the American people, the British people, the French people," she said.

Mary Schiavo, a former inspector general for the U.S. Department of Transportation, said the effort isn't "entirely window dressing, because we have to do something."

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"But," she said, "there's much more that has to be done to keep people safe."

She says she worries about planes carrying ill passengers who may not be detected until after they get off the flight. By then, the plane may have already been prepared for another flight.

Health officials have warned the screenings will likely catch some people with fevers, but not Ebola, and could miss some with Ebola as symptoms can take up to 21 days to appear.

"No exit or entry screening will supplant the need for state and local health departments, for clinicians and for individuals to be aware and to think Ebola," Cetron said.

Outbreak in Africa

At least 8,399 people are believed to have contracted the disease as of October 7, according to the World Health Organization. Of those, 4,033 have died, the agency said.

Photos: The Ebola epidemic Photos: The Ebola epidemic An Ebola survivor participates in a study in Monrovia, Liberia, on June 17, 2015. The country launched a five-year study to unravel the mystery of the long-term health effects that plague survivors of the viral disease. Since the epidemic started more than a year ago in a remote village in Guinea, more than 11,000 people have died, the vast majority in three West African nations, according to the latest numbers from the World Health Organization . And that number is believed to be low, since there was widespread under-reporting of cases, according to WHO. Hide Caption 1 of 45 Photos: The Ebola epidemic Women in Monrovia celebrate after the World Health Organization declared Liberia Ebola-free on May 9, 2015. Other cases have recurred since, however. Two people in Liberia have died of the disease since the end of June, just weeks after the WHO declared the nation free of the disease. Hide Caption 2 of 45 Photos: The Ebola epidemic A man walks past an Ebola awareness painting in Monrovia on March 22, 2015. Hide Caption 3 of 45 Photos: The Ebola epidemic Soldiers from the U.S. Army's 101st Airborne Division walk across the tarmac at Campbell Army Airfield before reuniting with their families at a homecoming ceremony March 21, 2015 in Fort Campbell, Kentucky. The 162 soldiers were deployed in Liberia, where they helped fight the spread of Ebola. Hide Caption 4 of 45 Photos: The Ebola epidemic Relatives weep for a loved one who it was believed died from Ebola, at a graveyard on the outskirts of Monrovia on March 11, 2015. Hide Caption 5 of 45 Photos: The Ebola epidemic Doctors Without Borders staffer Alex Eilert Paulsen watches as mattresses and bed frames burn at the Ebola Treatment Unit in Paynesville, Liberia, on January 31, 2015. The organization reduced its number of beds from 250 to 30 as gains were made in battling the virus. Hide Caption 6 of 45 Photos: The Ebola epidemic Pauline Cafferkey, a Scottish woman diagnosed with Ebola, is put on a plane in Glasgow, Scotland, on December 30, 2014. Cafferkey, a 39-year-old nurse who volunteered in Sierra Leone, was being transported to London for treatment. Hide Caption 7 of 45 Photos: The Ebola epidemic A child who survived the Ebola virus is fed by another survivor at a treatment center on the outskirts of Freetown, Sierra Leone, on November 11, 2014. Hide Caption 8 of 45 Photos: The Ebola epidemic Health workers in Monrovia cover the body of a man suspected of dying from the Ebola virus on October 31, 2014. Hide Caption 9 of 45 Photos: The Ebola epidemic Kaci Hickox leaves her home in Fort Kent, Maine, to take a bike ride with her boyfriend on October 30, 2014. Hickox, a nurse, recently returned to the United States from West Africa, where she treated Ebola victims. State authorities wanted her to avoid public places for 21 days -- the virus' incubation period. But Hickox, who twice tested negative for Ebola, said she would defy efforts to keep her quarantined at home. Hide Caption 10 of 45 Photos: The Ebola epidemic Health officials in Nairobi, Kenya, prepare to screen passengers arriving at the Jomo Kenyatta International Airport on October 28, 2014. Hide Caption 11 of 45 Photos: The Ebola epidemic U.S. President Barack Obama hugs Ebola survivor Nina Pham in the Oval Office of the White House on October 24, 2014. Pham, one of two Dallas nurses diagnosed with the virus, was declared Ebola-free after being treated at a hospital in Bethesda, Maryland. The other nurse, Amber Vinson (not pictured), was treated in Atlanta and also declared Ebola-free. Hide Caption 12 of 45 Photos: The Ebola epidemic Health workers in Port Loko, Sierra Leone, transport the body of a person who is suspected to have died of Ebola on October 21, 2014. Hide Caption 13 of 45 Photos: The Ebola epidemic Health workers bury a body on the outskirts of Monrovia on October 20, 2014. Hide Caption 14 of 45 Photos: The Ebola epidemic Garteh Korkoryah, center, is comforted during a memorial service for her son, Thomas Eric Duncan, on October 18, 2014, in Salisbury, North Carolina. Duncan, a 42-year-old Liberian citizen, died October 8 in a Dallas hospital. He was in the country to visit his son and his son's mother, and he was the first person in the United States to be diagnosed with Ebola. Hide Caption 15 of 45 Photos: The Ebola epidemic Boys run from blowing dust as a U.S. military aircraft leaves the construction site of an Ebola treatment center in Tubmanburg, Liberia, on October 15, 2014. Hide Caption 16 of 45 Photos: The Ebola epidemic Aid workers from the Liberian Medical Renaissance League stage an Ebola awareness event October 15, 2014, in Monrovia. The group performs street dramas throughout Monrovia to educate the public on Ebola symptoms and how to handle people who are infected with the virus. Hide Caption 17 of 45 Photos: The Ebola epidemic Ebola survivors prepare to leave a Doctors Without Borders treatment center after recovering from the virus in Paynesville, Liberia, on October 12, 2014. Hide Caption 18 of 45 Photos: The Ebola epidemic A man dressed in protective clothing treats the front porch of a Dallas apartment on October 12, 2014. The apartment is home to one of the two nurses who were diagnosed with Ebola after treating Thomas Eric Duncan, a Liberian national who traveled to Dallas and later died from the virus. Hide Caption 19 of 45 Photos: The Ebola epidemic A woman crawls toward the body of her sister as a burial team takes her away for cremation October 10, 2014, in Monrovia. The sister had died from Ebola earlier in the morning while trying to walk to a treatment center, according to her relatives. Hide Caption 20 of 45 Photos: The Ebola epidemic A man digs a grave on October 7, 2014, outside an Ebola treatment center near Gbarnga, Liberia. Hide Caption 21 of 45 Photos: The Ebola epidemic A person peeks out from the Dallas apartment where Thomas Eric Duncan, the first person diagnosed with the Ebola virus in the United States, was staying on October 3, 2014. Hide Caption 22 of 45 Photos: The Ebola epidemic A girl cries as community activists approach her outside her Monrovia home on October 2, 2014, a day after her mother was taken to an Ebola ward. Hide Caption 23 of 45 Photos: The Ebola epidemic A health official uses a thermometer September 29, 2014, to screen a Ukrainian crew member on the deck of a cargo ship at the Apapa port in Lagos, Nigeria. Hide Caption 24 of 45 Photos: The Ebola epidemic Workers move a building into place as part of a new Ebola treatment center in Monrovia on September 28, 2014. Hide Caption 25 of 45 Photos: The Ebola epidemic Medics load an Ebola patient onto a plane at Sierra Leone's Freetown-Lungi International Airport on September 22, 2014. Hide Caption 26 of 45 Photos: The Ebola epidemic A few people are seen in Freetown during a three-day nationwide lockdown on September 21, 2014. In an attempt to curb the spread of the Ebola virus, people in Sierra Leone were told to stay in their homes. Hide Caption 27 of 45 Photos: The Ebola epidemic Supplies wait to be loaded onto an aircraft at New York's John F. Kennedy International Airport on September 20, 2014. It was the largest single shipment of aid to the Ebola zone to date, and it was coordinated by the Clinton Global Initiative and other U.S. aid organizations. Hide Caption 28 of 45 Photos: The Ebola epidemic A child stops on a Monrovia street September 12, 2014, to look at a man who is suspected of suffering from Ebola. Hide Caption 29 of 45 Photos: The Ebola epidemic After an Ebola case was confirmed in Senegal, people load cars with household items as they prepare to cross into Guinea from the border town of Diaobe, Senegal, on September 3, 2014. Hide Caption 30 of 45 Photos: The Ebola epidemic A health worker wearing a protective suit conducts an Ebola prevention drill at the port in Monrovia on August 29, 2014. Hide Caption 31 of 45 Photos: The Ebola epidemic A burial team from the Liberian Ministry of Health unloads bodies of Ebola victims onto a funeral pyre at a crematorium in Marshall, Liberia, on August 22, 2014. Hide Caption 32 of 45 Photos: The Ebola epidemic Dr. Kent Brantly leaves Emory University Hospital on August 21, 2014, after being declared no longer infectious from the Ebola virus. Brantly was one of two American missionaries brought to Emory for treatment of the deadly virus. Hide Caption 33 of 45 Photos: The Ebola epidemic An Ebola Task Force soldier beats a local resident while enforcing a quarantine on the West Point slum on August 20, 2014. Hide Caption 34 of 45 Photos: The Ebola epidemic Local residents gather around a very sick Saah Exco, 10, in a back alley of the West Point slum on August 19, 2014. The boy was one of the patients that was pulled out of a holding center for suspected Ebola patients after the facility was overrun and closed by a mob on August 16. A local clinic then refused to treat Saah, according to residents, because of the danger of infection. Although he was never tested for Ebola, Saah's mother and brother died in the holding center. Hide Caption 35 of 45 Photos: The Ebola epidemic Workers prepare the new Ebola treatment center on August 17, 2014. Hide Caption 36 of 45 Photos: The Ebola epidemic Liberian police depart after firing shots in the air while trying to protect an Ebola burial team in the West Point slum of Monrovia on August 16, 2014. A crowd of several hundred local residents reportedly drove away the burial team and their police escort. The mob then forced open an Ebola isolation ward and took patients out, saying the Ebola epidemic is a hoax. Hide Caption 37 of 45 Photos: The Ebola epidemic A health worker disinfects a corpse after a man died in a classroom being used as an Ebola isolation ward August 15, 2014, in Monrovia. Hide Caption 38 of 45 Photos: The Ebola epidemic Aid worker Nancy Writebol, wearing a protective suit, gets wheeled on a gurney into Emory University Hospital in Atlanta on August 5, 2014. A medical plane flew Writebol from Liberia to the United States after she and her colleague Dr. Kent Brantly were infected with the Ebola virus in the West African country. Hide Caption 39 of 45 Photos: The Ebola epidemic Members of Doctors Without Borders adjust tents in the isolation area in Kailahun on July 20, 2014. Hide Caption 40 of 45 Photos: The Ebola epidemic Boots dry in the Ebola treatment center in Kailahun on July 20, 2014. Hide Caption 41 of 45 Photos: The Ebola epidemic Dr. Jose Rovira of the World Health Organization takes a swab from a suspected Ebola victim in Pendembu, Sierra Leone, on July 18, 2014. Hide Caption 42 of 45 Photos: The Ebola epidemic Red Cross volunteers disinfect each other with chlorine after removing the body of an Ebola victim from a house in Pendembu on July 18, 2014. Hide Caption 43 of 45 Photos: The Ebola epidemic A scientist separates blood cells from plasma cells to isolate any Ebola RNA and test for the virus April 3, 2014, at the European Mobile Laboratory in Gueckedou, Guinea. Hide Caption 44 of 45 Photos: The Ebola epidemic Health specialists work March 31, 2014, at an isolation ward for patients at the facility in southern Guinea. Hide Caption 45 of 45

Among health care workers fighting the outbreak, 416 are believed to have caught the disease and 233 have died, according to WHO.

The numbers were reported from Guinea, Liberia, Nigeria, Senegal, Sierra Leone, Spain and the United States.

American cases

Aid workers Nancy Writebol and Dr. Kent Brantly contracted the disease in Liberia while working with Samaritan's Purse to care for Ebola patients. They were flown to Emory Hospital in Atlanta, where they were treated and released in August after doctors concluded they were healthy.

A third patient, Dr. Rick Sacra, was flown to Omaha, Nebraska, after contracting the disease while working in Liberia. He was discharged in September.

Doctors at the same hospital are now caring for Ashoka Mukpo , an NBC News videographer diagnosed with Ebola on October 2.

Mukpo's condition continues to improve, according to a statement from The Nebraska Medical Center.

"Mr. Mukpo is still very weak, but his condition has improved since yesterday," said Dr. Phil Smith, medical director of the Biocontainment Unit at The Nebraska Medical Center. "He's eating some solid food now, so we're still headed in the right direction. ... The severity and unknown aspects of the disease we're dealing with always have to be kept in mind."

Mukpo has received the experimental drug Brincidofovir, along with a blood transfusion from Brantly, an Ebola survivor, the statement said.

Authorities imposed a mandatory quarantine on NBC News staffers who worked with Mukpo after the workers violated a voluntary quarantine, New Jersey health officials said.

Mukpo was among a team working with Dr. Nancy Snyderman , the news agency's chief medical correspondent.

"The NBC crew remains symptom-free, so there is no reason for concern of exposure to the community," said Donna Leusner, a spokeswoman for the New Jersey Department of Health.

In other countries

Morocco

The Confederation of African Football said the 2015 African Cup of Nations, a soccer competition, will go ahead as scheduled despite fears about Ebola by Morocco. The competition is scheduled to be held in Morocco from January 17 to February 8.

"CAF has registered the request and wishes to state that there are no changes of the schedules of its competitions and events," the group said in a statement released Saturday. "It must be noted that since the first edition in 1957, the Africa Cup of Nations has never witnessed a deferral or a change in schedule."

The CAF said it took into account recommendations from the World Health Organization and other medical experts.

United Kingdom

In London, the UK Department of Health said enhanced screening will be implemented at London's Heathrow and Gatwick airports and Eurostar terminals.

The screenings will involve assessing passengers' recent travel history, who they have been in contact with and onward travel arrangements, the department said.

English medical professionals, such as doctors and ambulance drivers, participated in a nationwide drill on Saturday on the handling of Ebola cases.

Spain

Teresa Romero Ramos , a nurse's assistant in Spain who is the first person to contract Ebola outside Africa, has been treated with the anti-influenza drug Avigan, hospital sources with knowledge of the case said Saturday.

Romero was in "stable but serious" condition Saturday after taking a turn for the worse earlier in the week, according to the hospital sources.

"Teresa is conscious and talking," a hospital source said.

special committee created by the Spanish government to tackle the Ebola crisis reported no significant changes in her condition Saturday, according to the Carlos III hospital spokeswoman.

After the nurse's assistant was diagnosed with Ebola, 16 people related to the case were being monitored in a Madrid hospital, including an emergency room doctor, the neighborhood doctor who saw her before the case was confirmed, and the nurse's husband, according to a government source. Those being monitored also included three people admitted to Hospital Carlos III Friday night -- a beautician, a nurse and a hospital cleaner.

"There has not been any change worth mentioning relating to those admitted, and they all remain asymptomatic," the special committee said.

The nurse admitted to the hospital Friday was told she needs to remain there for 21 days, a man who identified himself as her father said Saturday. The nurse, a friend of Romero, works at the same hospital as the nurse's assistent, Alcorcon hospital

"She is fine, no symptoms," her father said, adding that he hasn't seen her. He said he "just brought some things for her. When the doctors come in they wear the protective suits."

Another nurse under observation tested negative for the Ebola virus, the committee said Saturday. The nurse has been discharged but will remain under observation outside the hospital until her quarantine ends on October 16, the committee said.

Romero became sick after she helped treat an Ebola-stricken Spanish missionary. Her case has prompted questions from her fellow medical professionals about whether they are properly equipped to safely treat Ebola patients, and about why a week passed before she was treated.

But experts from the European Centre for Disease Prevention and Control who visited the hospital over the past three days said in the "procedure and action" carried out at the hospital complied with established protocols.

The statement added, "The current infrastructure is not designed to deal with this type of emergency. Nevertheless, the action and measures which have been taken, and which continue to be taken at present, are likely to improve it."

Russia

Russia plans to introduce Ebola vaccines within the next six months, the country's health minister said, according to Russian state news agency Ria Novosti.

"We are now creating three vaccines... and they will be created, we think, in the next six months," Health Minister Veronika Skvortsova said, according to Ria Novosti.

Skvortsova also said Russia is working on creating special drugs to be used in preventing and treating Ebola, the news agency reported.