RML researcher Andrea Marzi

National Institutes of Health Rocky Mountain Laboratories staff scientist Andrea Marzi was part of team of researchers who recently completed a study that showed a candidate Ebola vaccine was effective when diluted up to a million times in macaque monkeys. 

Last summer, the World Health Organization began drawing up plans to give reduced doses of the Ebola vaccine in the event that a long-running outbreak continued to stretch supplies in the Democratic Republic of the Congo.

Authorities there worried that if the outbreak worsened, there might not be enough of the vaccine to contain the spread of the disease.

The results of a recently published study completed by the National Institute of Allergy and Infectious Diseases’ Rocky Mountain Laboratories in Hamilton could offer hope for easing that fear in the future. The study’s findings suggest the current dose being used in Africa might be able to be highly diluted and still protect people against the deadly disease.

RML scientists showed that a dose that’s approximately one-millionth of what’s currently used to help control the spread of the disease in Africa protected experimentally infected macaque monkeys.

While it’s still too early to determine what that means for humans, the study’s lead author, Dr. Andrea Marzi, said the findings were encouraging.

The Ebola virus causes blood vessels to leak, which leads to a circulatory failure that starves the body’s organs of oxygen. Patients go into shock when organs begin to fail. The disease is spread via direct person-to-person contact through infected blood, sweat and vomit.

Marzi said the current Ebola vaccine is a genetically modified live vesicular stomatitis virus that includes one protein of the Ebola virus. That single protein generates a protective immune response against the Ebola virus to those who receive the vaccine.

“The vaccine itself is still a replicating virus, but it only has one small component of the Ebola virus in it,” she said. “It’s all that the body of a person needs to generate that protective immune response.”

The vaccine can cause some minor adverse reactions like a headache, fever, chills and myalgia (muscle aches and pains), but Marzi said those reactions are “nothing worse” than what people report after receiving a flu shot or yellow fever vaccination.

RML scientist Dr. Heinz Feldman led the project to design the Ebola vaccine currently being used in Africa while he was still working at Canada’s National Microbiology Laboratory. Feldman now leads RML’s virology laboratory that completed the vaccine dosage study using macaques that was recently published in EBioMedicine.

Marzi said it’s one of several studies the Hamilton research team has completed on the vaccine over the years, including one published in 2015 that showed the time between vaccination and protection from the deadly disease occurred in a week.

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The vaccine is currently unlicensed. The manufacturer has submitted a biologics license application to the U.S. Food and Drug Administration.

Marzi said the VSV-Ebola vaccine was first used in the later part of 2014 during an Ebola outbreak in West Africa that claimed about 11,000 lives.

“There were only limited doses for human use at that point,” she said.

In 2015, the vaccine was used again during an outbreak in Guinea. In that country, health workers performed a ring vaccination trial that provided vaccine to anyone in direct contact with an infected person to slow the spread of the disease.

After learning about the potential of a vaccine shortage in the Democratic Republic of the Congo, Marzi said RML researchers decided to test the efficacy of a diluted version of the vaccine.

“We thought that if we could dilute it just 10 times, it could make a tremendous difference,” she said. “If we had 100,000 doses available and we dilute it 10 times, we could vaccinate a million people. Our intention was to see if a 1-in-10 dilution could help in countering a potential vaccine shortage.”

“Our study snowballed from there,” Marzi said.

The researchers found that a dose of about one-millionth of what is being used today in the Congo was enough to protect experimentally infected monkeys from the disease.

“It was definitely a surprise for Heinz and me,” she said. “I clearly did not expect that.”

Many research and clinical studies must still be completed before any changes would be recommended for humans. That work would not be completed at RML, Marzi said.

“You can’t make any recommendations from this one study,” she said. “That’s something we wouldn’t do here. We do hope the scientific community will see this…and might consider reducing the dose in another clinical trial.”