Vaccines for preventing malaria (pre-erythrocytic)

Abstract

Malaria is a parasitic disease spread by mosquitoes. It affects millions of people worldwide and causes significant illness and mortality. The symptoms of uncomplicated malaria include fever, headache, muscle pain, and vomiting; and children commonly present also with rapid breathing, cough, and convulsions. Severe malaria leads to unconsciousness and death. Uncomplicated malaria can almost always be cured with appropriate drugs, given soon after symptoms appear, but in small children in particular, progression and death can come within 48 hours. The hope − bolstered by several decades of increasingly promising research − remains that one or more vaccines to prevent malaria will augment the existing malaria control tools. The expectation is that successful vaccines will decrease malaria incidence, but because of the complexity of the organism and other factors, protection will not be complete. The malaria parasite develops through several phases in the human body that evoke different immunologic responses, and vaccines for all phases are under development. This review looks at vaccines targeted at the 'pre-erythrocytic' phase of the parasite's life, the phase before the parasites first enter the bloodstream from the liver. Trials of four types of vaccine against P. falciparum, the most important human malaria species, were available for this review. One of these (the RTS,S vaccine) significantly reduced the number of episodes of clinical malaria and severe malaria in children, while the other three vaccines were not effective under the conditions of the trials. No severe adverse events observed following the RTS,S vaccination were judged to be related to vaccination, though minor adverse events like headache, swelling, and malaise were