The World Health Organization declared it's ethical to use untested drugs and vaccines in the ongoing Ebola outbreak in West Africa, although the tiny supply of one experimental treatment has been depleted and it could be many months until more is available.
The last of the drug is on its way to Liberia for two stricken doctors, according to a UK-based public relations firm representing Liberia.
The US company that makes it said the supply is now "exhausted." Later Tuesday, Canada said it would provide some of its experimental Ebola vaccine for use in West Africa.
A Spanish missionary priest who died Tuesday in Madrid was the third person to receive the experimental treatment called ZMapp. Two US aid workers who received it in recent weeks are said to be improving.
The outbreak, the biggest in history, has killed more than 1,000 people in Guinea, Sierra Leone, Liberia and Nigeria.
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There is no proven treatment or vaccine for Ebola; several are in early stages of development. ZMapp, made by Mapp Pharmaceuticals, is so new that it has never been tested in humans, although an early version worked in some monkeys infected with Ebola. It's aimed at boosting the immune system's efforts to fight off Ebola.
"If there are drugs that can save lives - as animal studies have suggested - shouldn't we use them to save lives?" Dr. Marie-Paule Kieny, an assistant director-general at WHO, told a Geneva press conference Tuesday.
But it is "very important to not give false hope to anybody that Ebola can be treated now. This is absolutely not the case," she added.
ZMapp is made in tobacco plants, and US officials have estimated that only a modest amount could be produced in two or three months, unless some way to speed up production is found.
The UN health agency says 1,013 people have died so far in the Ebola outbreak in West Africa of the 1,848 suspected or confirmed cases recorded by authorities. The killer virus is spread by direct contact with bodily fluids like blood, diarrhea and vomit.
Canada announced it would donate 800 to 1,000 doses of its experimental Ebola vaccine developed by the Public Health Agency of Canada. A small supply will be kept in Canada in case any is needed there. The vaccine has not been tested in humans, but has shown promise in animals.
Read: Who gets experimental Ebola drug?
"The trouble is, of course, with this very, very limited number of vaccines, who would you give that to?" said Dr. Gregory Taylor, deputy head of the agency.
He said the agency has been advised that it makes the most sense to give the vaccine to health care workers in Africa. They are among the most vulnerable because of their close contact with Ebola patients. Several doctors and nurses have died in the outbreak.
The same vaccine was actually used once in 2009. It was rushed to a German lab worker who pricked her gloved finger with a needle that had contained Ebola. She survived, though it wasn't known if she was ever really infected with Ebola and if the vaccine worked.
Some experts aren't convinced, though, that any novel drugs or vaccines would make a difference in ending the current outbreak.
Once they're put to the test, most experimental drugs that seemed promising in animal studies "don't turn out to benefit people," said Dr. Jesse Goodman, former chief scientist for the US Food and Drug Administration, now at Georgetown University Medical Center.
He said some drugs prove harmful. "Unless we can ascertain that carefully, how do we really help people in the long run?"
After the two Americans received the experimental drug ZMapp, officials in Liberia requested it. Officials in Sierra Leone and Guinea have expressed interest in getting experimental treatments but haven't yet asked.
"The Liberians can count on their government, but Guineans can only count on God in the face of Ebola," said Assiatou Diallo, a nurse in Conakry, Guinea's capital.
The Spanish missionary, 75-year-old Miguel Pajares, died in Madrid's Carlos III Hospital, the hospital and his order said. A doctor who was part of the team treating the priest confirmed he had received the experimental drug.
The doctor, an infectious diseases specialist, spoke on condition of anonymity, not being authorized to discuss the treatment.
Pajares' body will be cremated Wednesday to avoid any public health risks, the hospital said. He had worked for the San Juan de Dios hospital order, a Catholic group, helping to treat people with Ebola in Liberia when he became ill and was evacuated.
The son of the US missionary aid worker being treated for Ebola at an Atlanta hospital said his mother is doing well. Jeremy Writebol told NBC's "Today" show in an interview broadcast Tuesday that Nancy Writebol's eyes are getting brighter and she's even joking a little.
Jeremy Writebol said he had been concerned his mother might not make it when she was taken out of an ambulance at Emory University's hospital last week after being flown from Liberia. A second American, Dr. Kent Brantly, had been able to walk from the ambulance into the hospital.
Writebol said doctors have said they expect her to recover, though they haven't elaborated.
WHO said the size of the outbreak - the first in West Africa - made the experimental use of drugs ethical even though there is no evidence they work and it is possible they could be dangerous. The agency convened an expert panel of ethicists, infectious disease experts and patient representatives to discuss the issue on Monday.
"We don't have enough people to rely on the traditional methods if we want to stop the outbreak as soon as possible," Kieny said.
WHO said it was OK to use unproven treatments or vaccines if patients give their informed consent and are guaranteed confidentiality and freedom of choice.
There was no specific advice on who should get them; the panel only said more analysis and discussion was needed.
"I don't think there could be any fair distribution of something available in such small quantities," Kieny noted.
She said some companies were speeding up trials of their new Ebola vaccines and there might be some preliminary safety data by the end of the year.
WHO also said the world had "a moral duty" to collect evidence about the safety and effectiveness of Ebola treatments in scientific trials.
Canada's Tekmira Pharmaceuticals Corp. is developing a drug that targets Ebola's genetic material. The FDA had halted a small safety study with questions about a reaction in healthy volunteers.
Last week, Tekmira announced that the FDA had modified its restriction, clearing a roadblock to possible experimental use in patients, and said it was "carefully evaluating options."
West African nations are struggling to control both the deadly outbreak and the fear it has created. Some airlines flying in and out of the region have suspended flights.
The Ivory Coast, which shares borders with Liberia and Guinea, banned direct flights from those countries and said it would increase health inspections at its borders. Guinea-Bissau also announced it was temporarily closing its border with Guinea because of the Ebola outbreak.
On Tuesday, Liberian President Ellen Johnson Sirleaf suspended all travel by executive branch officials for one month. She also ordered those already abroad to return home within a week "or be considered as abandoning their jobs," according to a statement.
Read: 5 things to know about Ebola outbreak in West Africa