Malaria Vaccine Success Hailed as Breakthrough

Could save lives of millions of children in developing world

FRIDAY, Oct. 15, 2004 (HealthDayNews) -- It's been a long, tough fight, but researchers say results of a major malaria vaccine trial mean science may be winning the war against a disease that claims millions of lives each year.

"This is the first convincing evidence that a malaria vaccine can be produced that can impact disease in children living in Africa," said study co-researcher Dr. Filip Dubovsky, of the Malaria Vaccine Initiative, which helped fund the study.

At a press conference Oct. 14 in London, Dubovsky and his co-researchers unveiled the results of a study conducted with more than 2,000 Mozambique children 4 years of age and under. Half of the children received three doses of an experimental vaccine, RTS,S/AS02A, while the other half did not.

Observing the children for six months after vaccination, Dubovsky reported that "the vaccine reduced the risk of developing the disease by 29.9 percent," while cutting the incidence of severe, life-threatening malaria episodes by 58 percent.

"This should be celebrated as a major advance," said Allan Saul, co-chief of the Malaria Vaccine Development Unit at the National Institute of Allergy and Infectious Diseases.

"What's great about it is that it demonstrates that, by reducing malaria transmission, you can make a significant difference for the health of kids in Africa," he said.

The findings appear in the Oct. 16 issue of The Lancet.

Malaria infection in humans is caused by the transmission, via mosquito bite, of the microscopic Plasmodium falciparum parasite. At the beginning of the infection process, the parasite first takes up residence in the liver. In this short, pre-symptomatic phase -- called the pre-erythrocytic stage -- the parasite replicates before moving into the bloodstream. Once in the bloodstream, it begins its assault on blood cells, triggering symptoms such as chills, fever and headache.

Dubovsky said the RTS,S/AS02A vaccine is targeted at the early, pre-erythrocytic stage of infection -- inhibiting the parasite's spread by generating immune antibodies and stimulating "killer white cells" to wipe out the microscopic invader. The vaccine's aim is to kill the parasite before it can develop further and cause symptomatic disease, he said.

The success of this trial -- which Dubovsky described as "the largest pediatric malaria vaccine trial done in Africa" -- has long been a Holy Grail for experts bent on defeating malaria, which kills between 1 million and 3 million people each year, mostly young children.

The disease also leads to incalculable amounts of suffering, primarily among people living in poverty in the developing world. Experts estimate that more than 500 million acute episodes of debilitating malaria sickness occur throughout the world each year.

Malaria is also a major drain on the already fragile health services of Africa and other developing regions, said Dr. Lee Hall, chief of the Malaria Vaccine Development Section of the Extramural Arm of NIAID. But he said that's another reason to be encouraged by the results of this study.

"They actually got a 35 percent reduction in [malaria-related] hospital admissions, and it almost achieved statistical significance," Hall noted. "If this finding is borne out and you consider that in Africa somewhere between 20 to 50 percent of all hospital admissions are due to malaria, that would be tremendous in terms of the impact it could have, not only in saving children's lives, but in its economic impact."

All of the experts agreed that more research needs to be done to make sure RTS,S/AS02A works in other geographical areas and under different conditions. But the vaccine has already generated interest from its manufacturer, drug giant GlaxoSmithKline, and Dubovsky said that, "if everything goes very well with this vaccine, it could be licensed by the end of the decade."

RTS,S/AS02A is just one of more than 25 different malaria vaccine candidates currently in the pipeline, according to the World Health Organization.

For its part, the Malaria Vaccine Initiative -- which receives much of its funding from the Bill and Melinda Gates Foundation -- "is supporting over a dozen different malaria vaccine candidates," Dubovsky said. "These may be part of a solution as standalone vaccines or as improvements to this vaccine."

Saul said the success of the Mozambique study is sure to encourage researchers working on other vaccines.

"We've now got proof in principle that this thing can work, so that ought to stimulate people to put even more effort into this, because there's now a higher possibility of success," he said. "I think we should really understand that this is a major milestone in the development of a malaria vaccine."

More information

To learn more about ongoing research in the fight against malaria, visit the Malaria Vaccine Initiative.

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