SOME said it couldn鈥檛 be done. But after decades of failure, researchers have finally produced a malaria vaccine that could save many lives, even though it is only partly effective.
The challenge now is to build on this success to produce better vaccines. The hope is that if other experimental vaccines also turn out to be at least partly effective, they could be combined to make a far more effective vaccine. The need is great: malaria affects half the world鈥檚 population and kills a million children a year.
The experimental vaccine, known only as RTS,S/AS02A targets Plasmodium falciparum, the most dangerous malaria parasite. A trial in Mozambique involving more than 2000 children aged 1 to 4 shows that it reduces the risk of infection by 30 per cent. And for those who still get infected, it reduces the chances of developing the most severe form of malaria by 58 per cent.
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It works even better in children aged 2 or under, reducing their risk of severe disease by 77 per cent (The Lancet, vol 364, p 1411). That is encouraging, since the ultimate aim is to vaccinate all infants at risk. 鈥淭his is clearly the best result we鈥檝e seen with a candidate malaria vaccine,鈥� the head of the trial team, Pedro Alonso of the Hospital Clinic of the University of Barcelona in Spain, told a press briefing last week.
鈥淭he idea is that first, we test them separately. Then, if they work, we could try them together鈥�
A larger trial will begin soon. But it may be 2010 before the vaccine is approved and ready for use.
The MVI paid GlaxoSmithKline to develop the vaccine, with the help of the Gates Foundation, and sponsored the trials. The results so far are especially impressive given that the vaccine targets just one surface feature of the parasite, which is present only during the first stage of infection, says Melinda Moree, director of the international Malaria Vaccine Initiative. Vaccines against other stages of the parasite鈥檚 complex life cycle are in the first stages of trials. If any work, they could be combined with RTS,S/AS02A to create a multistage vaccine.
The ME-TRAP vaccine against the liver stage of the life cycle has already shown promise in early trials in the Gambia. 鈥淓xpect more news at the end of the year,鈥� says Adrian Hill of Oxford University, head of the ME-TRAP team. And a trial of a vaccine against the lethal blood stage of the parasite鈥檚 life cycle is due to begin early next year in Kenya. The MSP-1 vaccine has been developed by the Walter Reed Army Institute of Research in Forest Glen, Maryland.
鈥淭he idea is that first we test them separately. Then, if they work, we could try them together,鈥� says Marie-Paule Kieny, director of the initiative for vaccine research at the World Health Organization in Geneva. But there is no guarantee the strategy will work. 鈥淚f you mix too many components, you might get interference,鈥� she says.