A Liberian man walk past an Ebola awareness painting on a wall in downtown Monrovia, Liberia. Picture: EPA
Two experimental Ebola vaccines can safely elicit immune responses by one month after initial vaccination that last for at least one year, results from a large clinical trial in Liberia showed Wednesday. 

The trial, published in the New England Journal of Medicine and conducted by a U.S.-Liberia clinical research collaboration, involved 1,500 healthy adults who were rapidly enrolled at Redemption Hospital in Monrovia, the capital of Liberia, in early 2015 during the West Africa Ebola outbreak. 

Three groups of 500 volunteers received one of the experimental vaccines or a placebo, and they all provided blood samples before vaccination and again at one week, one month, six months and one year post-vaccination. 

The vaccines included cAd3-EBOZ, co-developed by the U.S. National Institute of Allergy and Infectious Diseases (NIAID) and GlaxoSmithKline; and rVSV-ZEBOV, which was initially engineered by scientists from the Public Health Agency of Canada and is now licensed to Merck Sharp & Dohme Corp., a subsidiary of Merck. Blood sample testing showed that responses at one week were modest with both vaccines but 71 percent of cAd3-EBOZ recipients and 84 percent of rVSV-ZEBOV recipients developed an antibody response by one month. 

At one year, 64 percent of cAd3-EBOZ recipients and 80 percent of rVSV-ZEBOV recipients still had an antibody response, indicating that antibody responses were largely maintained in both groups. 

Some participants who received the investigational vaccines experienced mild to moderate side effects that resolved, such as headache, muscle pain, feverishness and fatigue. 

Overall, investigators did not identify any major safety concerns related to the vaccines. Most of the serious medical issues reported during the trial were due to malaria. "This clinical trial has yielded valuable information that is essential for the continued development of these two Ebola vaccine candidates and also demonstrates that well-designed, ethically sound clinical research can be conducted during an epidemic," Anthony Fauci, director of the NIAID, which sponsored the trial, said in a statement. 

"A safe and effective vaccine would be a critically important addition to classical public health measures in controlling inevitable future Ebola outbreaks," Fauci said. Ebola virus disease is a severe, often fatal illness in humans. The virus is transmitted to people from wild animals and spreads in the human population through human-to-human transmission. Currently, no Ebola vaccines have been licensed for use in humans.