(CNN) About nine months ago, Pauline Cafferkey was discharged from a London hospital -- seemingly signaling her victory in beating Ebola .

Now, not only is Cafferkey back in the hospital with a rare relapse of the deadly virus, but she's gotten worse.

London's Royal Free Hospital announced Wednesday afternoon that "Cafferkey's condition has deteriorated and she is now critically ill."

The hospital didn't elaborate on the news about the Scottish nurse, who last year became the first person diagnosed with Ebola in the United Kingdom. But it's not a good sign, coming five days after the same medical facility confirmed Cafferkey had been transferred there from Queen Elizabeth University Hospital in Glasgow "due to an unusual late complication of her previous infection by the Ebola virus."

That day, the Royal Free Hospital indicated that Cafferkey was in "serious condition" and being treated in a "high-level isolation unit."

"Sad to hear of deterioration in Pauline Cafferkey's condition," UK Health Secretary Jeremy Hunt tweeted. "Thoughts & prayers with her & wonderful team looking after her @RoyalFreeNHS."

Sad to hear of deterioration in Pauline Cafferkey's condition. Thoughts & prayers with her & wonderful team looking after her @RoyalFreeNHS. — Jeremy Hunt (@Jeremy_Hunt) October 14, 2015

Since her January discharge, Cafferkey has been out and about, including receiving a Pride of Britain award late last month and paying a visit to 10 Downing Street, where pictures showed her with the prime minister's wife, Samantha Cameron.

Last week Dr. Emilia Crighton, director of public health for the National Health Service for Greater Glasgow and Clyde , insisted that the risk of the 39-year-old Cafferkey inadvertently passing on Ebola to anyone else was "very low."

"In line with normal procedures in cases such as this, we have identified a small number of close contacts of Pauline's that we will be following up as a precaution," Crighton said.

Went to Sierra Leone during Ebola outbreak

Like many other volunteers, Cafferkey had gone to West Africa knowing the dangers there. The Ebola virus had spread like wildfire, ultimately killing more than 11,000 people and infecting some 28,000, according to the World Health Organization

Yet that harsh reality didn't stop the public health nurse in Scotland's South Lanarkshire area from being part of a 30-person team deployed by the UK government to work in Sierra Leone with Save the Children.

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

She and other health care workers would later be credited with playing a significant part in corralling and ultimately ending the devastating outbreak.

But, as Cafferkey learned, it came at a cost.

She fell ill shortly after touching back down on UK soil. Her Ebola diagnosis came next, followed by intensive treatment at the Royal Free Hospital. That facility has an isolation unit tended by specially trained medical staff and a tent with controlled ventilation set up over the patient's bed.

Her road to recovery wasn't always smooth. The Royal Free Hospital at one point noted that her condition had "gradually deteriorated over ... two days" and that she was then critical

Agency: 58 had contact with symptomatic nurse

She had good reason to celebrate September 28. That night she was honored at the Pride of Britain awards, a star-studded event (with this year's celebrities including soccer star David Beckham and Rupert Grint of "Harry Potter" fame) honoring good deeds around the country, spokeswoman Elizabeth Holloway told CNN.

The next day, Cafferkey joined other honorees at the Prime Minister's residence.

Less than a week later, on October 5, she went to a doctor in Glasgow because she felt sick, said a spokesperson for NHS Greater Glasgow and Clyde, who was not named per policy. Cafferkey was sent home, only to be admitted the next day to Queen Elizabeth University Hospital in the Scottish city.

Holloway said no one associated with the Pride of Britain awards is being monitored for possible Ebola, because Cafferkey wasn't showing any signs of illness at the time. Ebola only spreads when there's direct contact with the bodily fluids of an infected person who is displaying symptoms of the disease.

In a statement, NHS Greater Glasgow and Clyde said that health authorities have identified 58 people who had been in close contact with Cafferkey since she became symptomatic. Forty of those who'd had direct contact with her bodily fluids were offered an Ebola vaccine; 25 of them accepted while 15 declined, according to the health agency.

And yes, tests earlier this year indicated the nurse wasn't showing signs of Ebola. But that doesn't mean that traces of the virus can't linger -- if not in the blood, then perhaps elsewhere in the body.

Her relapse is also proof that the Ebola fight isn't totally over, one week after WHO reported the first week since March 2014 with no new cases.

U.S. doctor had traces of Ebola in eye months later

According to the WHO, Cafferkey was then and is still the lone Ebola case in the United Kingdom.

Her relapse does not represent "a new case of Ebola (but rather) is a complication of her previous illness," Scotland's chief medical officer said Friday. It's a rare thing, but not necessarily unprecedented.

JUST WATCHED Why his eye turned from blue to green Replay More Videos ... MUST WATCH Why his eye turned from blue to green 05:14

American doctor Ian Crozier was treated for Ebola in Atlanta last year and declared free of the virus in his blood.

Despite the presence of the virus, samples from tears and the outer eye membrane tested negative, which meant the patient was not at risk of spreading the disease during casual contact, the hospital said at the time.

Crozier received steroids and an antiviral agent, and his eye gradually returned to normal. His case prompted a warning to doctors to watch Ebola survivors for eye problems.