Why isn't there a malaria vaccine...?

Malaria kills more than one million people a year and developing a successful vaccine against it has been the target of rigorous and determined research for decades. While positive strides have been made, success in the form of a comprehensive vaccine continues to elude scientists for many reasons. 

The malaria parasite, transmitted to humans by the female Anopheles mosquito, is a more complex “bug” than most, and has several radically different forms physiologically and morphologically. It constantly changes once in the bloodstream, mutating and building resistance to drugs to which it is vulnerable for only a tiny window of time. Furthermore, there is currently no vaccine against a parasite. Vaccines are based on triggering an immune response in humans that is known to protect against an infection but there is no such response to malaria in humans, at least not one that totally protects against the parasite.

While the genomes of both the parasite and the mosquito vector have been mapped, it will take decades and huge financial resources to make progress on determining what genes should be targeted. Additionally, experimental vaccines can’t be tested on animals because they are not sickened by the human plasmodium, therefore vaccines must be tested on humans. Current vaccine trials have proven only marginally effective, and prevention, mainly in the form of mosquito netting, remains the best approach to keeping people safe from malaria.