Another Shot at a Malaria Vaccine

Malaria, an infectious disease caused by Plasmodium parasites that are transmitted by mosquito bite, has a devastating global impact, causing 300 to 500 million clinical cases and up to 800,000 deaths each year. Vaccine development for malaria is marked by many failures, some encouraging successes, and much hope. Recently, a malaria vaccine candidate (RTS,S/AS01) based on the major surface protein of the transmissible sporozoite form of the parasite advanced into phase three clinical trials in Africa, and preliminary data show 55% efficacy against malaria episodes and 35% efficacy against severe malaria (1). Although it is not yet known how long protection lasts, this vaccine constitutes a milestone for developing a more efficacious vaccine. A highly protective vaccine that prevents malaria infection will also prevent disease and further transmission by the mosquito and, hence, constitutes the potential “magic bullet” in our future armamentarium against malaria. Yet developing such a vaccine has been frustratingly difficult. On page 475 of this issue, Epstein et al. (2) report the results of a clinical trial with an injectable preparation of Plasmodium sporozoites, attenuated by exposure to DNA-damaging irradiation and intended to prevent infection. Their trial results mark an inflection point in malaria vaccine development.