The studies in Liberia are taking place after smaller tests determined that the vaccines were safe for human use. By comparing them now with a dummy shot, scientists hope to learn whether they can prevent people from contracting the ghastly virus that has killed some 60 per cent of those hospitalized.
Yet despite the vaccine study's promise, authorities still must combat fear and suspicion that people could become infected by taking part. Each vaccine uses a different virus to carry non-infectious Ebola genetic material into the body and spark an immune response.
On Sunday in one densely populated neighbourhood of Monrovia, musicians sang songs explaining the purpose and intent of the trial in a bid to dispel fears.
B. Emmanuel Lansana, 43, a physician's assistant, was the first to receive doses on Monday. Two shots were administered at different points on his right arm. His wife had expressed apprehension about the vaccine trial, but Lansana said he still wanted to take part.
"From the counselling, all of the reservations I have were explained, my doubts were cleared," he said in a room where he was being observed for 30 minutes afterward.
Up to 600 volunteers are taking part in the first phase, and trial organizers have said eventually as many as 27,000 people could take part.
"We are targeting about 12 persons for today and hopefully the number will increase as we go along," Wissedi Sio Njoh, director of operation with the vaccination campaign, told The Associated Press.
The World Health Organization says the Ebola epidemic has infected more than 22,000 people and claimed more than 8,900 lives over the past year. Without a vaccine, officials have fought the outbreak with old-fashioned public health measures, including isolating the sick, tracking and quarantining those who had contact with them, and setting up teams to safely bury bodies.
Dr. Anthony Fauci, director of the U.S. National Institute of Allergy and Infectious Diseases, has said that both experimental vaccines showed promise in first-stage human safety tests. One was developed by the National Institutes of Health and is being manufactured by GlaxoSmithKline. The other was developed by Canadian health officials and is licensed to two U.S. companies, NewLink Genetics and Merck.
The vaccine trials come as the three most affected countries — Guinea, Sierra Leone and Liberia — appear to be making strides against the Ebola epidemic first identified last March. The U.N. health agency said last week that the countries had reported fewer than 100 cases in the past week, for the first time since June.
Associated Press Medical Writer Lauran Neergaard in Washington and Krista Larson in Dakar, Senegal contributed to this report.