(CNN)The first doses of the Ebola vaccine were on a commercial flight to West Africa and were expected to arrive on Friday, according to a spokesperson from GlaxoSmithKline (GSK) one of the companies that has created the vaccine with the National Institutes of Health.
Another vaccine from Merck and NewLink will also be tested.
"Shipping the vaccine today is a major achievement and shows that we remain on track with the accelerated development of our candidate Ebola vaccine," Dr. Moncef Slaoui, chairman of global vaccines at GSK said in a company release.
In December, the trial of the vaccine made by Merck and NewLink were stopped after some of the volunteers in the trial had "transient mild" joint pain. After investigating that side effect, scientists concluded it was not a big enough issue to stop the development of the vaccine. No similar side effects were noted in the GSK trial.
There are other Ebola vaccines being tested by companies in the United States and in Russia.
This first shipment will be used, along with a placebo in this first large-scale trial in the next few weeks in Liberia.
"We are expecting to start by the last week in January, but there are some details that need to be ironed out regarding the FDA," said Dr. Anthony Fauci, the director of the National Institute of Allergy and Infectious Diseases (NIAID) at a press conference.
The tests should begin in the Monrovia area and will involve nearly 30,000 people. People who have had the virus and survived will be excluded from this trial, according to GSK.
The first people to get the vaccine will be health care workers who are some of the population that is most at risk for catching Ebola. That's because it can be easily transmitted through exposure to bodily fluids. In Liberia there have been 370 cases of health care workers becoming infected with Ebola, 178 of them have died according to the World Health Organization.
The number of newly infected health care workers has declined recently, as has the number of cases in general in Liberia.
In August and September of 2014 the WHO was seeing 300 new confirmed cases per week, versus the 8 new confirmed cases according to this latest incident report.
Another trial in Sierra Leone should start a few weeks after the trials get started in Liberia, according to the NIH.
Sierra Leone has had the largest number of infections of any country with 10,340 reported cases and 3,145 deaths from Ebola. The disease has slowed down according to the WHO, but still there were 117 new confirmed cases according to the latest report.
The Centers for Disease Control and Prevention will work with Sierra Leone's government to help manage the tests.
The NIH will also soon be testing the therapeutic drug ZMapp as early as next month.
ZMapp is an experimental drug that has been used to help patients who have already been infected by the virus. The drug maker, Mapp Biopharmaceutical ran out of the drug last year, but has been making enough doses for a small human trial.
The number of new Ebola cases in Liberia has been declining, but public health leaders say that there are still "little mini outbreaks" and that "until there is a very last case, (an epidemic) is not over until it is over," Fauci said.
Since the outbreak began in December 2013, there have been 21,759 infections and 8,668 people have died from Ebola.