An experimental malaria vaccine for babies reduced the chances of developing the mosquito-borne illness by more than half, scientists are reporting today. The results, from two trials conducted in Kenya and Tanzania, are the most promising yet in the quest to develop effective immunization against the life-threatening parasite.

The findings on GlaxoSmithKline's RTS,S/AS01 showed a 53 percent lower risk of infection over eight months and were presented today at the annual American Society for Tropical Medicine and Hygiene meeting in New Orleans. They build on results published last year that found that GSK's RTS,S/AS02 vaccine (the same shot formulated with a different adjuvant, or immune-enhancing additive) slashed the risk of a first-time malaria infection by 66 percent in infants who received the full three-dose course. A safety study on that vaccine published in today's online edition of the New England Journal of Medicine showed about the same efficacy — a 65 percent reduction in first-time infections for babies 12 months and younger.

Malaria causes between 350 million and 500 million illnesses every year, and kills about 1 million people — mostly infants and children in Africa, according to the Centers for Disease Control and Prevention (CDC).

GSK and the Bill & Melinda Gates Foundation paid for the vaccine research, which will total around $500 million by the end of the studies. GSK is planning a Phase III trial — the last needed before a drug is approved for marketing — next year, and if all goes well, the vaccine could be available by 2012, according to the Los Angeles Times. "We can begin to foresee the difference this scientific breakthrough could make in the lives of millions of African children who suffer and die from this disease year after year,” Joe Cohen, VP of research and development for emerging diseases and HIV at GSK Biologicals, said in a press release.

The results may be "extremely encouraging," but "we won't really know how effective this vaccine is until we complete the Phase III trials," Ripley Ballou, who oversees vaccine grants for the Gates Foundation, told the Seattle Post-Intelligencer. Those trials would involve many more children in multiple countries, he said.

Because the vaccine has only been shown to be partially protective so far, it wouldn’t be enough to wipe out the disease, Ballou added. "This could be a powerful tool," he told the newspaper, "but we will continue to have to use many tools, such as bed nets, to reduce the prevalence of malaria."

Image of child being vaccinated with RTS,S vaccine by John-Michael Maas/Darby Communications