NEWS - December 2001
Malaria vaccine moves ahead
One of the lucky few:
a child in Thailand is treated for severe malaria. Many children never get to hospital
A CANDIDATE vaccine that provides partial protection against malaria is to start trials in children in Mozambique next year. The announcement, from the international Malaria Vaccine Initiative at PATH (1) and the vaccine's developer GlaxoSmithKline, came this month as researchers reported that the vaccine reduced rates of infection in a group of adults in a trial in The Gambia (2) .
Although the protection is incomplete and shortlived, the evidence so far suggests the vaccine is more promising than most previous candidates, say researchers. "This is the first vaccine that has showed convincingly that you can protect people against malaria," says Adrian Hill of the University of Oxford, a member of the team involved in the Gambian trials. But the vaccine, called RTS,S/AS02, needs to be modified to make it longer-lasting and more powerful, he says.
Nevertheless scientists and public health officials believe that trials of the vaccine in children are justified, because it might offer more benefit to children than to adults. Children make up some 90% of the estimated one million people who die of malaria each year. Young children tend to suffer from more severe episodes of malaria than adults, because they have not yet built up an immune response to the parasite. If a vaccine provides even partial protection, it might allow children to build up some natural immunity while experiencing fewer, and milder, episodes of infection.
Malaria vaccines are notoriously difficult to develop, partly because the malaria parasite, Plasmodium falciparum, has a complex life cycle and presents different faces to the immune system. For malaria-endemic areas, scientists believe it will be important for vaccines to block infection by the parasite rather than merely reducing the symptoms of the disease. To do this, a vaccine needs to target the immature form of the parasite, the sporozoite, which enters the bloodstream from the bite of an infected mosquito. RTS,S/AS02 is made with a protein from the sporozoite, fused to the harmless surface antigen from the hepatitis B virus. In The Gambia, the vaccine protected 71% of men from infection in the first nine weeks after it was given, although protection waned to zero by sixteen weeks. Overall, the vaccine's efficacy over the period of the trial was 34%. The MVI project aims to increase the duration of protection and the efficacy of the vaccine.
Although GAVI will support some research and development, malaria vaccines are not currently receiving Alliance support because other players are funding them. The Alliance will instead focus its R&D resources on a limited number of products and technologies that are very close to market, such as vaccines against meningitis A, pneumococcus and rotavirus. But the Alliance considers the development of malaria vaccines to be a high priority for global health and its partners have welcomed the international support for the Mozambique trials of RTS,S/AS02.
(1) Clinical Trials of Advanced Malaria Vaccine Candidate Expand to Mozambique
(2) Bojang K. et al. Efficacy of RTS,S/AS02 malaria vaccine against Plasmodium falciparum infection in semi-immune adult men in The Gambia: a randomised trial. The Lancet, 2001; 358: 1927-34. Access for this paper at their website.
Immunization Focus December 2001 - Contents