In the first results from tests on an experimental Ebola vaccine, researchers at the National Institute of Allergy and Infectious Diseases (NIAID) report for the first time Wednesday that the shot is safe and that it leads to an immune response among healthy volunteers. The vaccine, developed by the National Institutes of Health and GlaxoSmithKline, was tested in 20 participants in the US at the NIH Clinical Center in Bethesda. 
 
 “This tells us that this is kind of a positive signal about moving to the next stage,” says Dr. Anthony Fauci, director of NIAID. 
 
 MORE: We’re Getting Closer to Vaccines and Drugs for Ebola 
 
 The vaccine is meant to protect uninfected people from Ebola, and, if effective, would be tested next in populations in high-risk areas such as west Africa, where the outbreak is ongoing, to immunize them against the virus. It does not contain live Ebola virus, but does contain snippets of its protein coat, just enough to alert the immune system to produce antibodies and immune cells that can recognize and destroy any live viruses that people might eventually encounter. The pieces of Ebola protein are introduced to the body via another virus, one related to the common cold that infects chimps. 
 
 The shot was tested in two doses among 10 people each; it triggered antibodies and immune cells that in primate studies were enough to protect them against a challenge of Ebola up to 10 months later. Whether that’s also the case among people won’t be known until the vaccine is tested among thousands more in west Africa, including health care workers and family members of ill patients, who are most vulnerable to getting exposed to the virus. 
 
 Only two people reported brief fevers after getting vaccinated. 
 
 MORE: Here’s How the Ebola Vaccine Trial Is Doing 
 
 The vaccine is one of two that scientists are preparing to test in the outbreak zone beginning in early 2015. Another candidate uses an entirely different approach involving a live Ebola virus that has been crippled so it can’t reproduce once it infects a person. The advantage to that system is that it might launch a stronger and more robust immune response than the NIAID and GSK shot, which may require a boost after several months to maintain strong immune protection against Ebola. “At the end of the day, you don’t know which is the most effective until you test them, and that’s the point,” says Fauci. ||||| A nurse in Switzerland holds a dose of experimental vaccine developed at the National Institutes of Health. (Photo: JEAN-CHRISTOPHE BOTT, EPA) 
 
 The first experimental Ebola vaccine to be tested in humans appears safe and capable of stimulating the immune system, according to a small, early clinical trial at the National Institutes of Health. 
 
 But the dose of vaccine required to spur the immune system into action is very high, which could make it harder for its manufacturer to quickly produce it, experts say. 
 
 Still, the results of the 20-person study, launched in September, are promising enough to proceed to a study in West Africa with thousands of participants, said Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases. These trials could take some time, because researchers will have to wait to see if people who are vaccinated contract Ebola. 
 
 The vaccine, developed by the NIH, uses a chimpanzee cold virus, called an adenovirus, to carry genes from two types of Ebola viruses into human cells, Fauci said. The vaccine – which will be manufactured by GlaxoSmithKline -- can't cause Ebola. It's also being tested in the United Kingdom, Mali and Switzerland. 
 
 The study found that all 20 people who received the vaccine made antibodies against Ebola, according to an article in The New England Journal of Medicine. Some people who got the vaccine also produced immune cells, called T-cells, that fight off infections. 
 
 People who got a higher dose of vaccine had a stronger immune response, the study says. The vaccine appeared safe. The only side effects were short-lived fevers in two people who received the higher dose. 
 
 Peter Hotez, dean of the National School of Tropical Medicine, said he's concerned that it took a high dose of vaccine to produce an immune system reaction. That could make it hard to produce enough of the vaccine to save lives in the West African outbreak, where Ebola has infected 15,351 people and killed 5,459, mostly in Guinea, Sierra Leone and Liberia. 
 
 The NIH vaccine appears to require tens of thousands more viral particles to stimulate the immune system than a rival vaccine, developed by the Public Health Agency of Canada, called the VSV vaccine, said Michael Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota. That vaccine uses vesicular stomatitis virus, which belongs to the same family as rabies, to carry Ebola genes into cells. Commercial rights to that vaccine have been sold to Merck. 
 
 "When time is of the essence, as it is during the current outbreak, the question is not, 'Can you make the vaccine?' but 'How soon can you make? And how much?' " Osterholm said. 
 
 Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, said quarantines may discourage health workers from traveling to West Africa. (Photo: Alex Wong, Getty Images) 
 
 Thomas Geisbert, an Ebola expert at the University of Texas Medical Branch in Galveston, expressed another concern. 
 
 In animal studies, the NIH vaccine didn't protect for very long, and required a booster to provide long-lasting protection. 
 
 Although scientists have been working on Ebola vaccines for years, it wasn't until the outbreak in West Africa that large pharmaceutical companies showed interest in developing vaccines and bringing them to market, Geisbert now. 
 
 Now, nine Ebola vaccines are being tested, Fauci told Congress last week. 
 
 The NIH and Canadian vaccines are the furthest along. 
 
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– The world took a small but significant step toward an Ebola vaccine today. Results of a study involving 20 people in the US found that the vaccine worked well enough to move on to round two—a much bigger test group of thousands of people in Africa, reports USA Today. If all goes well, that means the vaccine made by GlaxoSmithKline could be available in the second half of next year, reports the BBC. The National Institutes of Health reported the results today. "Whether it's a breakthrough depends on making sure that all the rest of data over the next few weeks and months is in line," says the chief executive of the drug-maker. "But this certainly gives us very significant cause for optimism." One drawback: It took high doses of the drug to trigger an immune response, which could eventually complicate mass production. One plus: The vaccine contains no live Ebola virus and can't cause the disease. A second vaccine candidate being tested does use live Ebola virus, but it's been "crippled so it can’t reproduce once it infects a person," explains Time.