New Yellow Fever Vaccine Shows Promise

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 April 07, 2011

A new vaccine for yellow fever is showing good results in tests as it overcomes one of the biggest problems with the current version.

Yellow fever is a deadly disease that occurs in much of South America and sub-Saharan Africa. A vaccine developed in the 1930s provides excellent protection, both for those living in affected areas and those traveling there. It's made using a live but weakened form of the yellow fever virus.

And that can lead to very serious side effects, says Thomas Monath of the U.S. biotech firm, Xcellerex.

"The problem is that in the last 10 years or so, we've discovered that the vaccine virus can cause a severe infection just like yellow fever itself," Monath explains."This occurs very rarely, but when it occurs, it is often fatal."

Monath is the lead author of a research paper describing the latest clinical trials of a new yellow-fever shot, developed to avoid even those very rare fatal complications. He says that, Instead of the live virus used in the current vaccine, the virus in the new vaccine is killed.

"We've inactivated it so it can't replicate and therefore it can't cause the severe infections of the brain or visceral organs, but it still can protect against infection."

So the researchers found that the new vaccine is safer - it produced limited, relatively mild side effects - while it stimulated the body's immune response. "And 100 percent of the volunteers developed what we call neutralizing antibodies, that neutralizes the virus, at a level that we believe to be protective," Monath says.

If final regulatory approval is granted, the new vaccine could be used both in countries where yellow fever is endemic, as well as for travelers visiting those areas. Pharmaceutical pricing is always hard to predict, but Monath says the new vaccine is likely to cost somewhat more than the current vaccine because it will be more expensive to make and because it's a better vaccine.

Thomas Monath's paper on the new yellow fever vaccine is published in the New England Journal of Medicine.