Malaria Vaccine Shows Promise

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New malaria vaccine raises high hopes

11:38 15 October 04

NewScientist.com news service

Prospects for a malaria vaccine have been boosted by “tantalising” results from a trial in 2000 children in Mozambique. Although the vaccine reduced the risk of infection by only 30% compared with a control vaccine - this is far better than any previous result.

“With 300 million people in Africa with malaria, a 30% reduction in infection is pretty substantial,” says Ripley Ballou, vice president of clinical development at GlaxoSmithKline (GSK), the company co-developing and testing the vaccine.

Even more impressive, say the investigators, is that the vaccine reduced the risk that the children - aged one to four - would develop the most severe and lethal form of malaria by 57%.

Better still, the risk of severe disease in recipients aged less than two saw a 77% reduction. The investigators are delighted by this because, ultimately, they want to give the vaccine to infants in their first year of life to maximise early protection.

Orders of magnitude

“We’ve found these results to be quite tantalising,” says Pedro Alonso of the Hospital Clinic of the University of Barcelona, and head of the team. “This is clearly the best result we’ve seen with a candidate malaria vaccine,” he said in a press briefing, organised by the international Malaria Vaccine Initiative, GSK and the Bill & Melinda Gates Foundation.

“We are talking orders of magnitude better than any previously tested vaccine,” added Ballou.

The vaccine attacks Plasmodium falciparum - the parasite which causes malaria - at the early infection stage, when it has just been injected into human blood by the bite of a carrier mosquito.

Unchallenged, the parasitic sporozoites make their way to the liver where they grow and mature into the merozoites. These are potentially lethal when released from the liver into the blood.

The vaccine, named RTS,S/AS02A carries two short proteins, called RTS and S, mimicking a key surface component of the sporozoite usually recognised by the immune system.

Incorporated into the empty shell of a hepatitis B vaccine, the new vaccine is thought to trigger production of antibodies and white blood cells that recognise and neutralise the sporozoites.

Manifestation decreased

“It works by preventing the parasite from emerging from the liver, or at least diminishing the load of parasites emerging,” says Joe Cohen, inventor of the vaccine at GSK.

“The next parasitic stages are controlled and manifestation of the disease is greatly decreased,” he adds.

The development partners hope to begin larger, phase III trials as soon as possible, working steadily towards the goal of a vaccine for infants. “One million children under five die each year from malaria,” says Melinda Moree of the Malaria Vaccine Initiative.

But it might take until 2010 to get the vaccine cleared and ready for use, warns Jean Stephenne, general manager of GSK Biologicals. And the price -estimated at $10 to $20 per vaccination - may be too much for some poorer nations unless richer countries help foot the bill.

“Far greater resources are still needed for malaria vaccine research,” said Regina Rabinovich of the Gates Foundation’s Global Health Program. “We should challenge world leaders to take malaria as seriously as they do AIDS.”

Journal reference: The Lancet (vol 364, p 1411)

Andy Coghlan