Finding a malaria vaccine that can confer full protection has been elusive until now. Intravenous injection of irradiated Plasmodium falciparum sporozoites, the infective stage of the malaria parasite, protected adults from malaria infection in a phase 1 trial. (Science http://dx.doi.org/10.1126/science.1241800)

Robert Seder and his colleagues showed that the sporozoite vaccine was safe when given 4–6 times intravenously, but full protection was only achieved in adults who received five doses, whereas three out of nine people who received four doses and five out of six nonvaccinated subjects developed malaria. It is unclear whether the different dosage schedule or the total number of parasites administered dictates the partial versus total level of protection. The vaccine elicited both sporozoite-specific antibody and cellular responses (of various types of lymphocytes) in a dose-dependent manner. However, the numbers of CD8+ T cells (which are thought to be required for protection from malaria infection) were low in the blood from some of the protected adults, and it is unclear whether antibodies contribute to protection.

Credit: London School of Hygiene & Tropical Medicine / Science Source

This vaccine provides proof of concept that protective immunity against malaria infection can be achieved through the intravenous administration of irradiated sporozoites, which could prevent infection in the liver and transmission of the malaria parasite. Future work should address how to implement this vaccination route in endemic areas (or how to find more feasible routes while maintaining efficacy) and how long this protection will last. This study also underscores the urgent need to define which immune responses and antigens confer protection in order to assess the efficacy of future malaria vaccines.