2007-10-20

An anti-malaria vaccine offering improved protection to children could be registered for use in four years, potentially saving millions of young lives, new research conducted in Mozambique has shown.

Scientists announced this week that a clinical trial involving 214 infants had confirmed the safety of the RTS,S/AS02D malaria vaccine. More children die of malaria than any other disease - over one million every year, most of whom are African children under five - and it is a major reason why Mozambique still has one of the world's highest child mortality rates, according to the UN Children's Fund (UNICEF).

Research by Dr Pedro Alonso, of the Manhica Health Research Centre, in Mozambique, and the Hospital Clinic of the Universitat de Barcelona, in Spain, and colleagues, indicated that the vaccine could reduce the risk of new infections by 65 percent. A previous trial in 2004 indicated 45 percent effectiveness for the same vaccine.

Global pharmaceutical company GlaxoSmithKline, with the help of the Malaria Vaccine Initiative by PATH, an international, non-profit health organisation, are developing it.

The children were randomly split into two groups, one assigned to receive three doses of the vaccine and the other to receive a hepatitis B vaccine as a control, at ages 10 weeks, 14 weeks and 18 weeks. Initial findings were published in the British medical journal, the Lancet.

Researchers said the candidate vaccine was "safe, well-tolerated and highly immunogenic [evoked a strong immune response] in young infants living in a rural area of southern Mozambique", and that the study had provided evidence of a strong association between vaccine-induced antibodies and a reduced risk of malaria infection.

"We have shown that a vaccine can reduce the risk of malaria infection in young African infants exposed to intense transmission of P. falciparum," the researchers said. Plasmodium falciparum is the most lethal of the four strains of the malaria parasite that infect humans: an initial severe infection can kill up to one in four victims unless they receive medical help.

The parasite has developed resistance to many of the older and cheaper drugs being phased out in line with World Health Organisation (WHO) guidelines, but only a tiny percentage of African children are treated with the new, more expensive and effective combination therapies.

First steps

The complex life cycle of the parasite, and its ability to remain undetected by the human immune system, means a long-lasting vaccine that is close to being totally effective is still many years away. The parasite also undergoes various changes as it develops in the mosquito - the vector, or main carrier, of the disease - as well as in the human liver, blood system, and red blood cells, making it difficult to target.

Vaccines in development tend to target different stages of the parasite's life cycle in humans, and the RTS,S/AS02D candidate vaccine aims to reduce its ability to infect and proliferate in the liver.

Repeated malarial infections result in a natural immunity if the person survives the first bouts. Adults and older children living in endemic malaria areas can show no clinical signs of the disease, even though they may be infected with the parasite. Older children may be more able to survive their first attack of malaria, which can damage the liver, kidneys and central nervous system, including the brain.

There is no easy way to fight malaria, but until the development of a vaccine that can totally prevent infection, preventing deaths by deferring infection among young children and reducing the severity of the disease are the best strategy.

According to the researchers, the vaccine would be effective as part of a layered strategy against malaria, including the provision of insecticide-treated bed nets (ITNs) and spraying insecticides to protect people against mosquitoes. According to the WHO, if used properly, ITNs can cut malaria transmission by at least 60 percent and child deaths by a fifth.

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