Malaria vaccines could make malaria nastier. In mice given an experimental vaccine now in trials, the malaria parasite evolved to get round the immunity – and in the process caused more severe disease.
Malaria kills 2000 children every day, sickens millions repeatedly, and helps keep tropical nations in poverty. Yet there is still no vaccine, partly because the parasite takes different forms as it moves from mosquitoes to human blood, to liver cells, red blood cells and back to mosquitoes.
One
malaria vaccine – RTS,S – is in
large-scale trials. It targets the liver stage of the parasite. Other vaccines in trials target the blood-cell stage, and contain a parasite protein called AMA-1, meant to prime the body's immune system to attack it.
These vaccines all seem likely to be "leaky", allowing vaccinated people to still acquire and transmit some parasites. Parasites that pass through vaccinated people this way could start resisting the vaccine in two ways, says
Andrew Read at Pennsylvania State University in University Park. The parasites' AMA-1 could change so that vaccine-induced immunity won't recognise it, a process called immune escape. Or parasites may emerge that dodge immunity in other ways, which could make the disease more virulent. ...
