The three-shot vaccine also reduced malaria outbreaks 35 percent after six months.
The trial, the results of which have been published in the British medical journal the Lancet and announced at a meeting in Seattle sponsored by the Bill & Melinda Gates Foundation, represents the first test of a malaria vaccine in young infants, the group most vulnerable to the effects of the parasitic disease.
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 on 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 '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.
Joe Cohen, GlaxoSmithKline's vice president for emerging diseases, HIV and vaccines research, said the vaccine worked by making antibodies that attacked the parasite as soon as it entered the body. It also encourages T cells, a type of white blood cell, to neutralize those parasites that escape the first barrage, he said.
The trial took place from June 2005 through March, and it involved two groups totaling 214 infants who received regular childhood vaccines. One group was randomly assigned to get the malaria vaccine at 10 weeks, 14 weeks and 18 weeks of age. The other group received the hepatitis B vaccine Energix-B.
The homes of all infants were sprayed with insecticide. Mothers were trained in the use of netting to keep out mosquitoes. "It's the combination of these things that is going to have the best chance of an impact," said James Burns, another malaria investigator at Drexel who was not involved in the study.
Researchers said they found no serious reactions from the vaccine.
"We are now a step closer" toward protecting young infants, said Pedro L. Alonso, head of the Barcelona Center for International Health Research at the University of Barcelona, who led the trial. "A great deal of work remains to be done." The Gates Foundation funded the trial through its Seattle-based PATH Malaria Vaccine Initiative, whose nonprofit mission is to speed promising vaccines to the developing world.
The Gates-based initiative has given GlaxoSmithKline $107 million to enable the company to finish work on the malaria vaccine, which had been languishing.
For its part, GlaxoSmithKline has spent more than 20 years and $300 million to create a malaria vaccine, Ballou said. The company, which has a U.S. headquarters in Philadelphia, expects to spend an additional $50 million to $100 million to finish this effort, he said. Work on the vaccine is being done at its GSK Biologicals division in Rixensart, Belgium.
Executives said it was premature to set a price for the vaccine, which still faces years of testing.
In a speech yesterday, Gates praised GlaxoSmithKline for assigning its top scientists to the project when they could be doing more lucrative work.
The quest for a vaccine represents a partnership between several African nations, the pharmaceutical industry and the PATH Malaria Vaccine Initiative (MVI).
Christian Loucq, director of MVI, said: "These results essentially provide another green light indicating that we can move toward a large Phase 3 trial with this vaccine."
That trial will begin next year in ten sites across sub-Saharan Africa and involve 10,000 thousand children.
If successful the vaccine will be licensed in 2011.
It would mark a hugely significant step forward in the fight against malaria.