The two vaccines, one from GlaxoSmithKline and the other from biotech start-up NewLink Genetics, "appear to be safe," the US National Institutes of Health (NIH) said.
The single injection vaccines proved safe for 600 participants, Fatorma Bolay from the Partnership for Research on Ebola Vaccines in Liberia said.
"We are grateful to the Liberian people who volunteered for this important clinical trial and encouraged by the study results," NIAID Director Dr Anthony Fauci said in a statement on Thursday.
"Now we must move forward to adapt and expand the study so that ultimately we can determine whether these experimental vaccines can protect against [the] Ebola virus disease and therefore be used in future Ebola outbreaks," Fauci added.
The trial began on February 2, in Monrovia, Liberia with over 2,600 people participating. Niether volunteers, nor researchers knew who received which vaccine, or the placebo saline injection.
Trial to be expanded
The encouraging results mean the trial will now be expanded to include about 30,000 people throughout the West African country.
Participants will be injected either with the GSK vaccine, the NewLink vaccine, or a placebo. Afterward, they will be assessed to see whether their immune systems have responded by producing anti-Ebola antibodies.
Volunteers will then be followed for at least a year, with blood samples being taken at six and 12 months after the vaccine to ascertain how long the immune response lasts.
Researchers hope to enroll more women in the next stage of the trial, as they only made up 16 percent of the first group, to ensure there are no-gender based differences in immune responses or side effects.
Trial participants are not intentionally exposed to the often-deadly virus. The response by a participant's immune system is considered an acceptable alternative to gauge the vaccine's effectiveness should someone be exposed to the virus.
British military nurse cured
Meanwhile, a British military nurse who contracted the virus while working in Sierra Leone has been successfully cleared of the Ebola virus after being treated with the MIL 77 drug.
Twenty-five-year-old Anna Cross was the first person in the world to be given the experimental drug, doctors at the Royal Free Hospital in the UK said at a press conference Friday.
However, doctors say it is too soon to know what role the drug played in Corporal Cross' recovery.
Liberia was one of the countries hardest hit by the Ebola virus, with 9,602 reported cases and 4,301 deaths, according to the World Health Organization (WHO). More than 24,927 people worldwide have been infected with the virus in the last 16 months, 10,338 have died in that period according to the WHO.
Guinea, where the epidemic broke out in December 2013, began an Ebola vaccine trial this week.
jlw/kms (AFP, dpa, Reuters)