A doctor in Kenya attends to a child sickened with malaria at a hospital that… (David Poland / PATH Malaria…)
A malaria vaccine under development has passed a critical milestone with researchers reporting Tuesday that the shots protect about half of all children from the disease.
The Phase 3 clinical trial was conducted among 6,000 sub-Saharan African children five to 17 months old who were given three doses. The vaccine is designed to prevent the malaria parasite from infecting, maturing and multiplying in the liver and reentering the bloodstream.
A malaria vaccine has been a goal for more than 20 years. The disease kills more than 1 million people each year -- mostly sub-Sahara African children younger than age 5. Those who don't die from the disease, which is transmitted by mosquitoes, can suffer severe illness.
Phase 2 results on the vaccine were published in 2004 and the new data confirm the earlier findings on safety and efficacy, said a principal investigator of the study, Dr. Tsiri Agbenyega of Ghana's University of Science and Technology, Kumasi.
After 12 months of follow-up, the study found a 56% reduction in the risk of developing malaria and a 47% reduction in severe malaria. The risk of side effects in the vaccinated children was similar to that for the control group.
"This translates to tens of thousands of malaria cases being abated," Agbenyega said at a news conference from Seattle, where the Malaria Forum was being hosted by the Bill & Melinda Gates Foundation. "Obviously, one would want to have higher efficacy when it comes to severe disease, but we are still hoping we can improve the efficacy of the vaccine."
Whether a vaccine with even 47% efficacy is good enough to get a vaccine to the marketplace is not yet clear, said Dr. Regina Rabinovich, director of the infectious diseases program at the Gates Foundation, which has provided key funding for the malaria vaccine initiative.
For decades, however, many health experts believed it was impossible to immunize against a parasitic infection, said Andrew Witty, chief executive of GlaxoSmithKline, whose company has partnered in developing the vaccine.
"We get used to seeing vaccines with 98% - 99% efficacy against common diseases in the West," he said. "It's really important not to just look at the percentages but to look at the absolute impact potential of the vaccine. Obviously, we will strive to improve the efficacy of the vaccine, but this is a good start."
Half of the world's population is exposed to malaria.
"This is one of the greatest scourges we face," Witty said.
The study found the risk reduction against severe malaria was only 34.8% when children ages 5 to 17 months were combined with another group of younger infants. But that figure is harder to analyze because of the combined age groups and variation in length of follow-up, said Dr. Mary Hamel, an investigator in the trial and chief of the malaria branch at the Kenya Medical Research Institute, U.S. Centers for Disease Control and Prevention.
Moreover, study participants also benefited from other malaria-control strategies, such as the use of bed nets and indoor spraying.
"This trial was conducted in the setting of good control measure and showed added benefit," Hamel said. "With this level of efficacy we can expect hundreds of thousands of lives to be saved."
The vaccine -- dubbed RTS,S -- is being developed by GSK and by the PATH Malaria Vaccine Initiative. Next year, a trial on the vaccine in infants 6 to 12 weeks old is due out, which is highly anticipated because, ideally, health officials would prefer to immunize infants when they receive other early-childhood vaccinations.
GSK is exploring how the vaccine could be delivered at the lowest possible cost, Witty said. The company has committed to selling the vaccine at a price equal to the cost of manufacturing it plus a 5% markup to be redeployed into further malaria research.
The scientific data were released online Tuesday in the New England Journal of Medicine.
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