Treatment: RTS,S/AS02A
Maker: GlaxoSmithKline Biologicals, the Walter Reed Army Institute of Research and the PATH Malaria Vaccine Initiative
Stage: Phase IIb, may enter phase III trials in 2008.

Why It Matters

Malaria is responsible for the deaths of more than two million people every year, more than half of whom are children in sub-Saharan Africa. No vaccine against the parasite is currently available commercially.

How It Works

RTS,S/AS02A fuses a cell surface protein found during the malaria parasite's infectious stage with a surface protein from hepatitis B, to help increase its ability to stimulate an effective immune response. This fusion protein is combined with an immune system booster consisting of an oil-in-water emulsion of a fat particle from the cell wall of salmonella bacteria and a plant-derived compound.

In its first phase IIb trial results, 1,442 children up to four years old received a three-dose regimen of the vaccine. After 18 months results showed the vaccine reduced clinical malaria episodes by one third and episodes of severe malaria by half.

Of all malaria vaccines, RTS,S/AS02A is the furthest along in clinical testing, "at least by four to five years," says Zarifah Reed at the World Health Organization's Initiative for Vaccine Research. Since RTS,S incorporates a hepatitis B antigen, it "will also be a hepatitis B vaccine," she adds. An estimated one million people die annually worldwide from hepatitis B and ensuing liver complications.

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