Progress and Challenges towards the Development of Malaria Vaccines

Abstract

The promise afforded by attenuated sporozoite vaccines in the 1970s led many researchers to believe that an efficacious malaria vaccine was an attainable medium-term goal. Over 30 years later, no licensed vaccine is currently available for public health intervention. This is despite global expenditure on research and development for malaria vaccines that is estimated to have increased from $US42 million in 1999 to $US84 million in 2004. Serious questions must therefore be asked: is this a good investment of research and public health funds, and are we really any nearer to producing a viable product for global use?Proponents of a malaria vaccine promote this technology as a viable way to combat both the current economic and humanitarian burden of malaria and the decreasing efficacy of many front-line antimalaria drug therapies. The recent successful phase IIb trial of the RTS,S/AS02A vaccine showed that the production of a subunit vaccine with significant efficacy is technically possible. The combined efforts and financial commitment of researchers, pharmaceutical companies, and not-for-profit organizations, including the Malaria Vaccines Initiative, have resulted in a significant scaling up in the number of products suitable for testing in humans. In addition, new technologies, such as genetically attenuated vaccines and the exploitation of malaria genomes, offer exciting possibilities for vaccine development. There is now a real possibility of producing a malaria vaccine licensed for public health. However, this positive outlook must be tempered with the challenges facing vaccine development and distribution. The efficacy levels seen with RTS,S/AS02A are well below those of all vaccines currently in use for public health. Furthermore, poor preclinical and clinical predictors of efficacy, allele-specific immunity, and an imperfect understanding of natural and induced immunity to malaria may yet delay (or even prevent) the development of a vaccine suitable for global use.