Three health care workers who were given the experimental Ebola drug ZMapp in Liberia have shown "very positive signs of recovery," the Liberian Ministry of Health said Tuesday.
Medical professionals treating the workers have called their progress "remarkable."
The good news comes as the number of deaths from the outbreak in West Africa climbed to 1,229, according to the World Health Organization.
The Liberian government also reported that all 17 patients who fled a local clinic after it was attacked earlier this week have been accounted for. Those who tested positive for Ebola are now being treated at another medical center.
The government met with local community leaders and concluded the attack stemmed from a misunderstanding; locals thought the clinic was "importing Ebola victims from the rest of the country," according to health officials. Looters who took a generator, mattresses and critical medical supplies have promised to return the items.
There are other small signs of hope amid the largest Ebola outbreak in recorded history. WHO has seen "encouraging signs" from Nigeria and Guinea that positive action can rein in the deadly disease. The current outbreak began in December.
The situation in Lagos, Nigeria, where the country's first case was detected in July, "looks reassuring," WHO said Tuesday.
"At present, the city's 12 confirmed cases are all part of a single chain of transmission. Those infected by the initial case include medical staff involved in his treatment, a patient in the same hospital, and a protocol officer in very close contact with the patient," the organization said.
No one on the same flight as the man who carried the infection into the country on July 20 was infected, despite him vomiting frequently on the flight and on arrival, it said. The man died July 25 and the 21-day incubation period has now passed, the WHO said.
Intensive efforts to track those at risk have not turned up any new cases outside the 12 identified.
One of those 12 has made a full recovery, the WHO said, which "counters the widespread perception that infection with the Ebola virus is invariably a death sentence." Evidence suggests early detection and therapy can help people survive, it said.
"The intensity of the search and monitoring effort raises cautious optimism that further spread of the virus in Nigeria can be stopped. The search for additional cases continues, as does the current high level of vigilance."
In Guinea, the situation is "is less alarming" than in Liberia and Sierra Leone, the WHO said, thanks to higher awareness and innovative efforts to contain the spread of the virus.
Community leaders have persuaded 26 villages that were resistant to outside help to cooperate, it said. As a result there has been a surge in reported cases -- but these are cases that were previously concealed, so they should not be seen as surge in infections.
But despite the positive signs, the WHO warned that the outbreak is not under control and that progress is fragile, with a real risk of another flare-up and the continued spread of the disease.
The WHO on Monday called on the affected countries to carry out exit screenings of travelers at international airports, seaports and major land crossings.
But it said it doesn't currently recommend travel restrictions and active screening of passengers on arrival in countries that don't have borders with the affected countries.