Written by Matthew Davis.
Over the past week there has been considerable discussion in the malaria research community about new data from a clinical trial of the world’s most advanced malaria vaccine that found it reduces malaria by about one third in African infants. A key issue has been whether this level of efficacy still would make the vaccine, called RTS,S, a big life-saver if it is added to childhood immunization programs in areas of Africa where the malaria burden is high.
But Monday at the ASTMH annual meeting in Atlanta, scientists were looking at a potential new role for RTS,S or other malaria vaccines. Could they be used in adults in areas like The Gambia where the disease burden is now relatively low as a tool to drive the disease to almost undetectable levels?
Umberto d’Alessandro, MD, MSc , PHD, is the theme leader for disease control and elimination at The Gambia Unit of the UK’s Medical Research Council. He discussed a proposal from the MRC to explore the potential of RTS,S in all age groups—by itself and along with the mass administration of anti-malaria drugs—to interrupt malaria transmission in The Gambia. (The administration of malaria drugs to numbers of people regardless of whether they are sick was a tactic used to fight malaria decades ago that is now being revived as a potential way to interrupt malaria transmission.)
D’Alessandro said his goal is to test strategies for “eliminating the remaining pockets” of disease in areas of Africa where interventions such as insecticide-treated bednets and indoor spraying with insecticides are pushing malaria transmission to record low levels.
He said the studies, if they proceed, envision initially evaluating the efficacy of RTS,S in about 1,000 adult volunteers at different dosages. D’Alessandro noted that studies in adults with an earlier version of the vaccine found relatively high levels of efficacy against malaria infection, though the protection lasted only for about nine weeks, then declined.
“If we could show significant protection against infection, we could then go to a larger trial and study the impact of mass vaccination alone or mass vaccination combined with mass drug administration,” he said.
Asked by a researcher in the audience why he was not proposing just mass drug administration by itself, d’Alessandro said he did not think that alone would be sufficient to interrupt transmission.
The discussion of a potential role for malaria vaccines in low transmission settings touched on some of the more confounding aspects of malaria in Africa, where deaths have fallen by one third over the last decade. Researchers acknowledged that it’s not always clear why the malaria transmission is going down in certain areas and not in others. While bednets and indoor spraying clearly have played a role, Azra C. Ghani, who studies transmission dynamics at Imperial College of London, said sometimes the factors remain unclear.
She said there are “places where interventions are widespread,” yet the disease burden remains high. Conversely, she said there are areas where there is low coverage with bednets and indoor spraying, but malaria transmission is falling.
Image: malaria researchers in Kenya via Flickr user US Army Africa.