CHICAGO -- A new vaccine showed promise at protecting young children from malaria, offering a potential new weapon against a disease that kills at least 1 million people each year, U.S. researchers said on Wednesday.

In a study of 100 West African children aged 1 to 6, the experimental vaccine produced immune responses similar to or even higher than those of adults infected by malaria all their lives.

The vaccine, which uses an immune system booster called an adjuvant from British drugmaker GlaxoSmithKline Plc (GSK.L)(GSK.N), targets the malaria parasite as it is actively infecting red blood cells and causing fever and illness.

This so-called blood stage vaccine acts at a later stage in the malaria parasite's life cycle than Glaxo's experimental vaccine Mosquirix.

"What jumps out to me about this vaccine is the antibody response," said Christopher Plowe of the University of Maryland in Baltimore and a Howard Hughes Medical Institute investigator whose study appears in PLoS ONE, a journal of the Public Library of Science.

"When you just look at the antibodies before you immunize anybody, the adults in Mali who have been exposed to malaria life-long, they don't get sick from malaria any more. They get infected but they don't get sick," Plowe said in a telephone interview.

"That is exactly what you want a blood stage vaccine to do."

SECOND ROUND OF TESTING

Plowe said children start out with fewer antibodies -- the immune system proteins that recognize invaders such as viruses or parasites. But after they were vaccinated, the children's antibody levels were just as high, or even a bit higher, than adults in their community.

The results were strong enough to start a second round of testing in 400 children to see if the vaccine can blunt the infection.

The new vaccine targets the malaria parasite after it has made its way though the bloodstream and into the liver, where it transforms into a new form called a merozoite, which can infect new red blood cells and cause fever and illness.

Plowe said he thinks the adjuvant from Glaxo, the same one used in Mosquirix, is priming the children's immune system to develop such a robust response.

"The hope would be that you could get two or more such first-generation vaccines, especially when you have the same adjuvant, and be able to come up with a multi-stage vaccine," he said.

Last month, Glaxo said Mosquirix is expected to complete late-stage testing in 2011 and, if proven effective, the company will seek regulatory approval by 2012.

Plowe's study was funded by the National Institute of Allergy and Infectious Diseases and the U.S. Agency for International Development. The vaccine was invented and made by the Walter Reed Army Institute of Research and formulated with an adjuvant by GlaxoSmithKline Biologicals.

Most of the 1 million or more people killed every year by malaria are young children and most live in Africa. The World Health Organisation says a child dies of malaria every 30 seconds. (Editing by Maggie Fox and John O'Callaghan)

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