One of the world's major killer disease that strikes mostly children living in tropical regions, malaria, is not controlled by an effective vaccine. An estimated 400,000 humans die annually of malaria--mostly in the tropics. Giant international drug companies are loath to spend the same amount as they do on cancer research or developing new analgesics to fund the development of an effective anti-malarial vaccine. The reason may be the potential market for such a drug: mostly developing nations whose citizens are poor.
Social Darwinism aside, there is some progress being made on finding an anti-malarial vaccine. Researchers from Australia have shown that children in Papua, New Guinea who have higher levels of Plasmodium falciparum antibodies specific to a short amino acid sequence of the parasite are protected against clinical or severe malaria. This antigen would be a good target for further vaccine say the study authors in the journal of the American Society for Microbiology, Infection and Immunity. The amino acid sequence known as ICAM1 is critical to P. falciparum's toxicity since it allows the parasite to bind to the brain's tiniest blood vessels, called microvasculature. There it remains undetected by the immune system causing cerebral damage by blocking blood flow and inflammation eventually leading to death of the host. [photo of P. falciparum gametocyte stages] The study followed 187 children 1-3 years old, measuring antibody responses to the ICAM sequence for sixteen months. Children with antibody responses were 37 less likely to develop severe malaria.
The most effective vaccine currently undergoing trials is RTS,S/ASO1. Third stage trials began in Sub-Saharan Africa in 2009. In children 5-17 months old four doses of the drug reduced malaria cases by 39%; severe cases were reduced by 31%. The European Medicines Agency issued a positive opinion on the drug's risk/benefit balance in 2015. Despite trial efforts in multiple countries including the US, there is currently no licensed malaria vaccine.