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Malaria vaccine trials promising

18th October 2006

02102006_malariaboy.jpgProspects for a malaria vaccine have been boosted by 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.

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.

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.

The development partners hope to begin larger, phase III trials as soon as possible, working steadily towards the goal of a vaccine for infants.

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.

Meanwhile, a new study by the London School of Hygiene and Tropical Medicine suggests that an effective way to treat pregnant women infected with malaria is with the use of older medications that have fallen out of use.

The study, which was conducted in Ghana between 2003 and 2004, separated pregnant women diagnosed with malaria into four trial branches and used different medications alone or in combination to see if any were suitable treatments. The study concluded that amodiaquine used alone or in combination with sulphadoxine-pyrimethamine (SP), was a safe and effective treatment for pregnant women.

The World Health Organisation (WHO) says that 30 million pregnant women in Africa live in malaria-endemic areas and that 200,000 newborns die each year due to malaria during pregnancy.

Artesunate-based combination therapy (ACT), the recommended first-line treatment for patients with malaria, has rarely been tested to see if it is safe for pregnant women.

Nine hundred women participated in the Ghana trial and all were at least 16 weeks pregnant and beyond the first trimester - when the effects of medication on the foetus can be the most harmful.

Amodiaquine fell out of use in the early 1990's when WHO withdrew recommendation for the drug. People were using it as a prophylaxis too frequently and experiencing side effects, such as liver toxicity and problems with their bone marrow. Amodiaquine was eventually re-introduced in the mid-1990's. Researchers wanted to see if it would be a more effective treatment than chloroquine, a drug to which malarial parasites are developing resistance.

WHO also recommends a preventative approach, which includes the use of insecticide-treated bednets and intermittent preventive treatment (IPT), whereby pregnant women are treated once a month for malaria during the last two trimesters of their pregnancy.


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Article Information

Title: Malaria vaccine trials promising
Author: Martine Hamilton
Article Id: 942
Date Added: 18th Oct 2006


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