A new Ebola vaccine being developed by drugmaker Profectus now has substantial data supporting its efficacy.

A report recently published in the journal Nature by author Dr. Thomas W. Geisbert of the University of Texas Medical Branch highlights the company's clinical trials testing the new vaccine on monkeys. Primates are always used in the first phases of testing a new vaccine before human trials since they most closely resemble humans more than any other lab animal.

Of the 10 monkeys used in the trial, eight were given the vaccine, while two did not receive the vaccine and were used as controls. Twenty-eight days after exposure to the virus, the two monkeys that had not received the vaccine died, while the eight that did receive the vaccine were healthy and appeared to be asymptomatic.

The vaccine was developed from an altered version of vesicular stomatitis virus, a disease that most commonly affects cows, in conjunction with a protein from the strain of the Ebola virus responsible for the recent outbreak in West Africa.

One of the chief concerns of this trial was to address the vaccine's side effects. An earlier version of the vaccine developed by Geisbert and the National Institute of Allergy and Infectious Diseases (NIAID) caused arthritis-like symptoms in a trial involving 40 healthy volunteers in Washington, D.C., bringing about safety concerns for the new version.

In an effort to curb the side effects caused by the previous version, two different vaccines — one containing a less attenuated version of VSV and one containing a highly attenuated version of VSV — were tested against each other in the most recent trial. The vaccine containing lower levels of the virus showed the same efficacy while successfully reducing side effects.

An even earlier version of the Ebola vaccine developed by Merck was tested on people infected with Ebola in Liberia and caused fever and joint pain. Although the side effects were not serious, the potential for those vaccinated to develop a fever was deemed to be potentially problematic during an outbreak since a fever is one of the first symptoms of the Ebola virus.

Geisbert believes the new vaccine has solved this issue and should not have the same effect once it is tested humans.

Profectus is the first company to publish data on the efficacy of their vaccine against the Ebola strain that is responsible for killing more than 10,000 people since 2013. The company has received $55 million in investment to develop the vaccine.

The newly published data and funding has positioned Profectus as the frontrunner in the race to develop an Ebola vaccine, but Merck and GlaxoSmithKline (and the NIAID) have also developed vaccines that are currently being used to fight the Ebola outbreak in West Africa.

It is currently unclear whether these companies are collecting data on their clinical trials in Africa, but even so, they will need to prove the efficacy of the vaccine in a lab in order to match the findings of Profectus to remain competitive.

Human trials of the vaccine are set begin in June, but Profectus does not foresee any safety concerns. A similar vaccine being developed by the company for HIV has been well-tolerated in test subjects.