Combining insecticide-treated bed nets with vaccines and other control measures may provide the best chance at eliminating malaria, which killed nearly 600,000 people worldwide in 2013, most of them African children.

More than 20 malaria vaccine candidates are in different stages of development, but none are licensed for use. So no one knows for sure what will happen when vaccines and bed nets are used together.

A University of Michigan-led research team used a mathematical model of malaria transmission to find out. The researchers examined potential interactions between the two control measures and found that – in some cases – the combination of bed nets and a vaccine actually makes the problem worse.

"The joint use of bed nets and vaccines will not always lead to consistent increases in the efficacy of malaria control. In some cases, the use of vaccines and bed nets may actually make the situation worse," said Mercedes Pascual, a professor in the U-M Department of Ecology and Evolutionary Biology.

"Specifically, our study suggests that the combined use of some malaria vaccines with bed nets can lead to increased morbidity and mortality in older age classes."

Pascual is co-author of a paper published online Jan. 19, 2015 in Proceedings of the National Academy of Sciences. The first author is Yael Artzy-Randrup of the University of Amsterdam, a former postdoctoral researcher in Pascual's lab. The other author is Andrew Dobson of Princeton University.

The malaria vaccines under development fall into three categories, each focusing on a different stage of the malaria life cycle. That cycle involves human hosts and Anopheles mosquitoes infected with Plasmodium parasites.

Preerythrocytic vaccines, or PEVs, aim to reduce the chances that a person will be infected when bitten by a disease-carrying mosquito. Blood-stage vaccines, or BSVs, don't block infection but try to reduce the level of disease severity and the number of fatalities.

Transmission-blocking vaccines, or TBVs, don't protect vaccinated individuals against infection or illness. But they prevent mosquitoes from spreading the disease to others after biting a vaccinated person.

Because TBV vaccines provide no protection to the vaccinated person but potentially reduce the rate at which others are infected, they are commonly called altruistic vaccines.

Pascual and her colleagues found that the combination of treated bed nets and TBV vaccines achieves the most efficient control, resulting in fewer cases of malaria while increasing the probability of eliminating the disease.

Read more: Michigan News press release

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