The study raises the prospect that hundreds of thousands of people worldwide could be helped if the vaccine becomes widely used.
But researchers said the vaccine's true value was still to be determined because the trial was focused more on safety than effectiveness. Even if these interim results hold up in subsequent tests, the vaccine will reduce deaths from malaria, not eradicate it.
"This is not a magic bullet," said Akhil Vaidya, a malaria researcher at the Drexel University College of Medicine and head of the Center for Molecular Parasitology, Microbiology and Immunology, who was not involved in the study. "We have a long way to bring the malaria down to acceptable levels. But if it's reduced by a few hundred thousand deaths, that will be a great achievement."
W. Ripley Ballou, GlaxoSmithKline P.L.C.'s vice president of new products for emerging diseases, said that a large trial to measure the vaccine's effectiveness was expected to start in late 2008 and that the company hoped to seek regulators' approval in 2011.
Malaria is a parasitic infection that enters humans through mosquito bites. The parasite kills more than one million people a year, mostly in sub-Saharan Africa, and infects more than 300 million annually.
It represents a confounding target for scientists. The parasite's genetic makeup is many times more complex than a virus. It mutates easily, enabling it to become resistant to existing drugs. And its exterior is coated with proteins that act like a biological shield, hiding it from the immune system.
