The vaccine known as RTS,S is made by the British pharmaceutical giant GlaxoSmithKline's lab in Belgium, and is the first of its kind to attempt to block a parasite, rather than bacteria or viruses.
Experts hailed the phase III trial under way at 11 sites in sub-Saharan Africa as a promising step toward eradicating the ancient mosquito-borne disease that kills almost 800,000 people yearly, most of them children.
The results are published online in the New England Journal of Medicine, and were simultaneously announced at the Malaria Forum hosted by the Bill & Melinda Gates Foundation in Seattle, Washington.
In a statement, philanthropist and Microsoft tycoon Bill Gates described the findings as a "huge milestone" in the fight against malaria, that "has the potential to protect millions of children and save thousands of lives."
Children aged five to 17 months who received three doses of the vaccine saw a 56 percent lower risk of developing clinical malaria, which causes high fever and chills, according to the study.
When it came to severe malaria -- the stage of the illness that can be fatal and reaches the blood, brain or kidneys -- those who received the vaccine showed a 47 percent lower risk.
"This is remarkable when you consider that there has never been a successful vaccine against a human parasite," said Tsiri Agbenyega, who chairs the RTS,S Clinical Trials Partnership and heads malaria research at Komfo-Anokye Teaching Hospital in Kumasi, Ghana.
"While these results are encouraging, we still have a ways to go," he told reporters.
The analysis was done with data from 6,000 children in the trial over a 12-month follow up after vaccination.
More data is needed from the younger age group -- infants aged six to 12 weeks -- to better assess how well it works in this particularly vulnerable group, experts said. Additional results from the younger set are due next year.
The World Health Organization says malaria claimed 781,000 lives in 2009. About 90 percent of malaria deaths each year occur in Africa and 92 percent of those are children less than five years old.
Asked whether the Gates Foundation would get behind a vaccine with a success rate of only about half, Regina Rabinovich, director for infectious diseases at the foundation's global health program, was circumspect.
"This is a key question. The group will ultimately want to understand efficacy, duration and safety," she said, adding she was "enthusiastic" about the results so far and was awaiting further data.
More than 15,000 children in seven African countries are enrolled in the trial, which is set to continue for two more years, and covers areas with other interventions in place against malaria, such as bed nets and spraying.
RTS,S was created in 1987 in GlaxoSmithKline Biologicals' lab in Belgium. Testing began on healthy adults in Europe and the United States in 1992, before the first Africa study started in Gambia in 1998.
Trial sites are now located in Burkina Faso, Gabon, Ghana, Kenya, Malawi, Mozambique and Tanzania, including 15,460 infants and young children in what GSK described as "the largest malaria vaccine trial to date."
The vaccine works by triggering the immune system to defend the body against Plasmodium falciparum, the deadliest type of malaria parasite.
Side effects included fever and swelling at injection site, "what you would typically see in other childhood vaccinations," said Agbenyega.
Read more at Discovery News
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