Two experimental Ebola vaccines appear to be safe based on evaluation in more than 600 people in Liberia who participated in the first stage of the Partnership for Research on Ebola Vaccines in Liberia (PREVAIL) Phase 2/3 clinical trial, according to interim findings from an independent Data and Safety Monitoring Board review. Based on these findings, the study, which is sponsored by the National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health, may now advance to Phase 3 testing.

A widely prescribed antidepressant, sertraline, commonly known as Zoloft, and Vascor, a drug used to treat high blood pressure, were found to block the spread of the virus in a study of mice, and researchers say they potentially could protect people exposed to Ebola.

WEDNESDAY, July 22, 2015 (HealthDay News) -- Researchers say they've made preliminary progress toward developing a drug that one day may treat people infected with the deadly Marburg virus, which is similar to Ebola.

Monkeys didn't die from Marburg virus after they were infected and then treated with the highest doses of the experimental drug. And healthy humans didn't get sick when they got similar doses, the researchers reported.

"These results have allowed us to predict a dose that could be expected to protect humans exposed to Marburg virus," said study author Dr. Alison Heald. She is a clinical associate professor with the division of allergy and infectious diseases at the University of Washington Medical Center, in Seattle.

The researchers emphasized that the drug is not a cure, and it's not known whether it will protect humans or what it might cost.

Marburg virus gets less attention than the Ebola virus since far fewer cases have been recorded. Only 572 cases of Marburg virus have ever been reported, compared to more than 27,000 cases of Ebola in the current outbreak in Africa alone, said Heald. She formerly was senior director of clinical development at Sarepta Therapeutics, which assisted in testing the experimental medication.

But the two viruses are very similar, Heald said. Both are highly deadly and cause a devastating condition known as viral hemorrhagic fever that can lead to massive bleeding and organ failure.

"Based on the similarity of Marburg and Ebola viruses and lack of available treatment options," Heald said, "it is certainly possible that Marburg virus could cause an outbreak of similar proportions to Ebola."

There's no specific treatment or vaccine for people infected with Marburg virus, which can be transmitted through contact with infected people.

The new drug, known as AVI-7288, does not prevent infection with Marburg virus. "Rather, it limits the replication of the virus, which in turn reduces the severity of disease once the virus is introduced into the body," explained study co-author Travis Warren. He is a research scientist with the U.S. Army Medical Research Institute of Infectious Diseases, in Frederick, Md.

In 2014, researchers at the University of Texas Medical Branch at Galveston reported success with an experimental Marburg drug that works in a similar way.

With the new drug, scientists injected the drug into monkeys infected with the Marburg virus and found they developed fewer symptoms, with none dying among those who got the highest doses.

The scientists also reported no safety problems when they gave healthy people doses similar to those that seemed to work in monkeys.

If it's ultimately used in the field, "AVI-7288 is mostly likely to be effective in treating those individuals who may have cared for or been exposed to someone infected with Marburg virus," Heald said. "It is not always clear when someone has been exposed to Marburg virus, but high-risk individuals could be monitored for early symptoms such that treatments could be started as early as possible."

Elke Muhlberger, an associate professor of microbiology who studies Marburg virus at Boston University School of Medicine, called the study findings "very exciting" and said the treatment could protect not only civilians but also health workers who may get infected through needle sticks.

But she cautioned that treating infected people may be challenging. When it comes to Ebola, she said, "People are afraid to go to the treatment units, and they only go when they are very ill." It takes about a week for the Marburg virus to incubate in the body, she said. By then, it may be too late for this drug to work.

Alan Schmaljohn, a professor of microbiology and immunology at University of Maryland School of Medicine in Baltimore, said "the study is a step in the right direction" and "and a hopeful sign that the drug can be tested in humans exposed to the virus without killing the subject outright."

The medication isn't approved for use by the U.S. Food and Drug Administration. And, it's not now under active development, said study co-author Dr. Michael Wong, senior medical director of infectious diseases at Sarepta Therapeutics, in Cambridge, Mass.

The study is published in the July 23 issue of The New England Journal of Medicine.

SOURCES: Alison Heald, M.D., clinical associate professor, division of infectious diseases, University of Washington Medical Center, Seattle; Michael Wong, M.D., senior medical director, infectious diseases, Sarepta Therapeutics, Cambridge, Mass.; Travis Warren, Ph.D., research scientist, U.S. Army Medical Research Institute of Infectious Diseases, Frederick, Md.; Elke Muhlberger, Ph.D., associate professor, microbiology, Boston University School of Medicine; Alan Schmaljohn, Ph.D., professor, microbiology and immunology, University of Maryland School of Medicine, Baltimore; July 23, 2015, The New England Journal of Medicine

GENEVA ¦ 31 JULY 2015 - Results from an interim analysis of the Guinea Phase III efficacy vaccine trial show that VSV-EBOV (Merck, Sharp & Dohme) is highly effective against Ebola. The independent body of international experts - the Data and Safety Monitoring Board – that conducted the review, advised that the trial should continue. Preliminary results from analyses of these interim data are published today in the British journal The Lancet.

"This is an extremely promising development," said Dr Margaret Chan, Director-General of the World Health Organization. "The credit goes to the Guinean Government, the people living in the communities and our partners in this project. An effective vaccine will be another very important tool for both current and future Ebola outbreaks."

While the vaccine up to now shows 100% efficacy in individuals, more conclusive evidence is needed on its capacity to protect populations through what is called “herd immunity”. To that end, the Guinean national regulatory authority and ethics review committee have approved continuation of the trial.