Combining insecticide-treated bed nets with vaccines may not provide the best chance at eliminating malaria, finds a study. Currently, over 20 malaria vaccine candidates are in different stages of development but none are licensed for use. 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 this 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, professor in the department of ecology and evolutionary biology.

The study suggests that the combined use of some malaria vaccines with bed nets can lead to increased morbidity and mortality in older age classes. “Ironically, the vaccines that work best with bed nets are the ones that do not protect the vaccinated host but, instead, block transmission of malaria in mosquitoes that have found an opportunity to bite vaccinated hosts,” Artzy-Randrup said.

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. In 2013, there were an estimated 198 million malaria cases worldwide, including 584,000 deaths, according to the World Health Organisation (WHO).

Most deaths occur among children living in Africa, where a child dies every minute from malaria, according to the WHO.