Two nurses infected with Ebola while caring for a dying patient in Dallas have been declared free of the virus.
One of them, Nina Pham, met President Barack Obama at the White House, hours after being discharged.
The governors of New York and New Jersey have ordered a mandatory 21-day quarantine period for anyone in contact with Ebola victims in West Africa.
The move comes a day after a doctor, Craig Spencer, returned from Guinea and tested positive for Ebola in New York.
Anyone arriving from affected West African countries without having had confirmed contact with Ebola victims will be subject to monitoring by public health officials.
The plans go beyond anything so far announced at a national level by the Obama administration.
People in New York City have expressed concern that Dr Spencer used public transport and restaurants before being diagnosed.
More than 4,800 people have died of Ebola - mainly in Liberia, Guinea and Sierra Leone - since March.
On Friday, it was announced that one million doses of an experimental Ebola vaccine will be produced by the end of 2015.
But it was a day of mixed news in the US, where the first infection in New York was followed by the release from hospital of Ms Pham, 26.
"I feel fortunate and blessed to be standing here today," she said. "I am on my way back to recovery."
Ms Pham thanked supporters for their prayers during her illness, and asked for privacy as she plans her return to Texas and a reunion with her dog, Bentley.
But first she was flown to Washington, at the request of the White House.
In other developments:
- the World Health Organization said "several hundred thousand" vaccine doses will be produced in the first half of 2015
- it also said vaccines could be offered to health workers in West Africa by December 2014
- dozens of people are being monitored in Mali after the country confirmed its first case of Ebola
- European Union leaders agreed to increase Ebola aid from 600m euros ($758m; £743m) to one billion
Ms Pham had been treated at a specialist hospital in Bethesda, Maryland, since being flown there from Texas Presbyterian Hospital in Dallas last week.
The other nurse, Amber Vinson, has also been declared virus-free, but she will remain in treatment in Atlanta until further notice.
"Tests no longer detect virus in her blood," a Georgia hospital official said.
Thomas Duncan died earlier this month and it is still unclear how the nurses contracted the virus while wearing protective clothing.
US Ebola patients:
Dr Kent Brantly: The aid worker was flown to Atlanta on 1 August and discharged three weeks later.
Nancy Writebol: Mr Brantly's colleague also contracted the virus in Liberia and also recovered.
Rick Sacra: After working in the same Liberian hospital, he recovered after treatment in Nebraska facility
Thomas Duncan: The Liberian was the first person diagnosed with Ebola inside the US. He died on 8 October.
Nina Pham: A nurse who treated Duncan in Dallas, she was declared free of the virus.
Amber Vinson: The second Dallas nurse is being treated in Atlanta, and about to be discharged.
Ashoka Mukpo: Freelance cameraman flown from Liberia to Nebraska and later released.
Dr Craig Spencer: A doctor recently returned from Guinea is in isolation at a New York city hospital.
The news of the two nurses' recoveries comes a day after a new infection, the first in New York.
Dr Spencer, 33, began to feel tired on Tuesday and developed a fever and diarrhoea on Thursday.
He immediately contacted medical services and was taken to the city's Bellevue Hospital, where he is being kept in isolation.
Mr Obama said his thoughts and prayers were with the patient.
On Friday, New York City Mayor Bill de Blasio said the city's response had been exemplary.
"We have this situation under control," Mr de Blasio told reporters. "Preparation levels were extraordinary."
He said New Yorkers had nothing to fear from the news.
"Casual contact cannot lead to acquiring this disease," he added, noting that only those in direct contact with infected bodily fluids were at risk.
But medical professionals have been retracing Dr Spencer's steps through the city, to further contain the outbreak.
He had travelled on the subway, been bowling and gone out jogging before he started feeling unwell.
His apartment in Upper Manhattan is being cleaned and the bowling alley in Brooklyn has been closed as a precaution.
Dr Spencer left Guinea on 14 October, and returned to New York City on 17 October via Europe.
His fiancee and two friends have been placed into quarantine.
Ebola patients are only infectious if they have symptoms, and the disease is only transmittable through bodily fluids, experts say.
Mr Obama telephoned both the mayor and the governor to discuss the deployment of health officials and to offer "any additional federal support necessary", the White House said.
The WHO says 443 health workers have contracted Ebola, of whom 244 have died.
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