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Credit: Caitlin Kleiboer
New research suggests that combining the use of malaria vaccines and insecticide-treated bed nets may actually increase the incidence of malaria.
The researchers used a mathematical model of malaria transmission to examine potential interactions between vaccines and bed nets.
They found that using insecticide-treated bed nets along with pre-erythrocytic vaccines (PEVs) or blood-stage vaccines (BSVs) increased the number of malaria cases.
However, using bed nets in conjunction with transmission-blocking vaccines (TBVs) resulted in fewer cases of malaria and increased the probability of eliminating the disease.
“The joint use of bed nets and vaccines will not always lead to consistent increases in the efficacy of malaria control,” said study author Mercedes Pascual, PhD, of the University of Michigan in Ann Arbor.
“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.”
Dr Pascual and her colleagues described this research in Proceedings of the National Academy of Sciences.
The team noted that the malaria vaccine candidates currently under development fall into 3 categories, each focusing on a different stage of the malaria life cycle.
PEVs aim to reduce the chances that a person will be infected when bitten by a disease-carrying mosquito. BSVs don’t block infection but try to reduce the level of disease severity and the number of fatalities.
And 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.
Dr Pascual and her colleagues found that using bed nets in communities treated with BSVs can increase levels of morbidity—to levels even higher than those expected in the absence of nets. Furthermore, BSVs can’t promote malaria elimination on their own.
PEVs can promote malaria elimination, but the researchers found regions of decreased morbidity when PEV vaccination levels were low and increased morbidity when PEV vaccination levels were high.
This suggests that higher levels of PEV coverage and bed net use could result in malaria elimination, but it would involve crossing a peak of enhanced morbidity.
Finally, the researchers found that using bed nets in communities treated with TBVs always leads to significant decreases in morbidity and increases the probability of malaria elimination.
“Ironically, the vaccines that work best with bed nets are the ones that do not protect the vaccinated host—the bed net does that—but instead block transmission of malaria in mosquitoes that have found an opportunity to bite vaccinated hosts,” said study author Yael Artzy-Randrup, PhD, of the University of Amsterdam in The Netherlands.
Unraveling the interactions between bed nets and vaccines is especially challenging due to the complex and transient nature of malaria immunity, the researchers noted.
A child’s first malaria infection can result in severe, sometimes fatal, illness. If the child survives, he or she will gain partial immunity that reduces the risk of severe illness in the future.
Additional bites from infected mosquitoes can help the child retain that immunity, which would otherwise wane after 1 to 2 years. But the combination of bed nets and certain vaccines can undermine that natural immunity.
“This complexity is at the heart of why it has been so hard to develop any sort of malaria vaccine,” said study author Andrew Dobson, DPhil, of Princeton University in New Jersey. 
Credit: Caitlin Kleiboer
New research suggests that combining the use of malaria vaccines and insecticide-treated bed nets may actually increase the incidence of malaria.
The researchers used a mathematical model of malaria transmission to examine potential interactions between vaccines and bed nets.
They found that using insecticide-treated bed nets along with pre-erythrocytic vaccines (PEVs) or blood-stage vaccines (BSVs) increased the number of malaria cases.
However, using bed nets in conjunction with transmission-blocking vaccines (TBVs) resulted in fewer cases of malaria and increased the probability of eliminating the disease.
“The joint use of bed nets and vaccines will not always lead to consistent increases in the efficacy of malaria control,” said study author Mercedes Pascual, PhD, of the University of Michigan in Ann Arbor.
“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.”
Dr Pascual and her colleagues described this research in Proceedings of the National Academy of Sciences.
The team noted that the malaria vaccine candidates currently under development fall into 3 categories, each focusing on a different stage of the malaria life cycle.
PEVs aim to reduce the chances that a person will be infected when bitten by a disease-carrying mosquito. BSVs don’t block infection but try to reduce the level of disease severity and the number of fatalities.
And 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.
Dr Pascual and her colleagues found that using bed nets in communities treated with BSVs can increase levels of morbidity—to levels even higher than those expected in the absence of nets. Furthermore, BSVs can’t promote malaria elimination on their own.
PEVs can promote malaria elimination, but the researchers found regions of decreased morbidity when PEV vaccination levels were low and increased morbidity when PEV vaccination levels were high.
This suggests that higher levels of PEV coverage and bed net use could result in malaria elimination, but it would involve crossing a peak of enhanced morbidity.
Finally, the researchers found that using bed nets in communities treated with TBVs always leads to significant decreases in morbidity and increases the probability of malaria elimination.
“Ironically, the vaccines that work best with bed nets are the ones that do not protect the vaccinated host—the bed net does that—but instead block transmission of malaria in mosquitoes that have found an opportunity to bite vaccinated hosts,” said study author Yael Artzy-Randrup, PhD, of the University of Amsterdam in The Netherlands.
Unraveling the interactions between bed nets and vaccines is especially challenging due to the complex and transient nature of malaria immunity, the researchers noted.
A child’s first malaria infection can result in severe, sometimes fatal, illness. If the child survives, he or she will gain partial immunity that reduces the risk of severe illness in the future.
Additional bites from infected mosquitoes can help the child retain that immunity, which would otherwise wane after 1 to 2 years. But the combination of bed nets and certain vaccines can undermine that natural immunity.
“This complexity is at the heart of why it has been so hard to develop any sort of malaria vaccine,” said study author Andrew Dobson, DPhil, of Princeton University in New Jersey.
Credit: Caitlin Kleiboer
New research suggests that combining the use of malaria vaccines and insecticide-treated bed nets may actually increase the incidence of malaria.
The researchers used a mathematical model of malaria transmission to examine potential interactions between vaccines and bed nets.
They found that using insecticide-treated bed nets along with pre-erythrocytic vaccines (PEVs) or blood-stage vaccines (BSVs) increased the number of malaria cases.
However, using bed nets in conjunction with transmission-blocking vaccines (TBVs) resulted in fewer cases of malaria and increased the probability of eliminating the disease.
“The joint use of bed nets and vaccines will not always lead to consistent increases in the efficacy of malaria control,” said study author Mercedes Pascual, PhD, of the University of Michigan in Ann Arbor.
“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.”
Dr Pascual and her colleagues described this research in Proceedings of the National Academy of Sciences.
The team noted that the malaria vaccine candidates currently under development fall into 3 categories, each focusing on a different stage of the malaria life cycle.
PEVs aim to reduce the chances that a person will be infected when bitten by a disease-carrying mosquito. BSVs don’t block infection but try to reduce the level of disease severity and the number of fatalities.
And 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.
Dr Pascual and her colleagues found that using bed nets in communities treated with BSVs can increase levels of morbidity—to levels even higher than those expected in the absence of nets. Furthermore, BSVs can’t promote malaria elimination on their own.
PEVs can promote malaria elimination, but the researchers found regions of decreased morbidity when PEV vaccination levels were low and increased morbidity when PEV vaccination levels were high.
This suggests that higher levels of PEV coverage and bed net use could result in malaria elimination, but it would involve crossing a peak of enhanced morbidity.
Finally, the researchers found that using bed nets in communities treated with TBVs always leads to significant decreases in morbidity and increases the probability of malaria elimination.
“Ironically, the vaccines that work best with bed nets are the ones that do not protect the vaccinated host—the bed net does that—but instead block transmission of malaria in mosquitoes that have found an opportunity to bite vaccinated hosts,” said study author Yael Artzy-Randrup, PhD, of the University of Amsterdam in The Netherlands.
Unraveling the interactions between bed nets and vaccines is especially challenging due to the complex and transient nature of malaria immunity, the researchers noted.
A child’s first malaria infection can result in severe, sometimes fatal, illness. If the child survives, he or she will gain partial immunity that reduces the risk of severe illness in the future.
Additional bites from infected mosquitoes can help the child retain that immunity, which would otherwise wane after 1 to 2 years. But the combination of bed nets and certain vaccines can undermine that natural immunity.
“This complexity is at the heart of why it has been so hard to develop any sort of malaria vaccine,” said study author Andrew Dobson, DPhil, of Princeton University in New Jersey.