The use of malaria vaccines combined with a bednet can be counter-productive in some cases and can even exacerbate the problem. This follows research carried out by an international team led by Yael Artzy-Randrup from the University of Amsterdam (UvA). The results are published online today in PNAS Online Edition.
The search for a malaria vaccine is seen as the Holy Grail in tropical medicine. However, vaccines do not provide us with a clear solution in the control of malaria. Scientists argue that future programmes have to take into account the complexities that may arise from combined methods of intervention.
There are currently more than 20 malaria vaccines in development, but because they cannot be used yet, nobody knows what happens when the vaccines are used in combination with bednets. The research team developed a scientific model to study the transmission of malaria. The researchers looked at possible interactions between the two methods of intervention and drew the conclusion that in some cases, the use of bednets in combination with vaccines only made the malaria problem worse.
The malaria vaccines that are currently in development can be divided into three categories: vaccines that prevent infection (preerythrocytic vaccines or PEVs); vaccines that don't prevent infection, but try to reduce the impact of the disease (blood-stage vaccines or BSVs); and vaccines that don't offer protection but simply prevent the malaria virus from spreading to others (transmission-blocking vaccines or TBVs).
Artzy-Randrup, Mercedes Pascual (University of Michigan, US) and Andy Dobson (Princeton University, US) found that a combination of pre-treated bednets and TBVs was the most effective control against malaria. This combination resulted in fewer cases of malaria whilst increasing the chance of eradicating the disease.
‘Oddly enough, it is the vaccines that don't actually provide direct protection that work best in combination with pre-treated bednets. The bednet protects us, whilst the vaccine ensures that the malaria virus isn't transmitted to the mosquitoes,’ according to Artzy-Randrup.
Malaria is a complex disease which means it is difficult to develop a strategy to control it. The disease can be very serious and even fatal for anyone contracting malaria for the first time. Survivors become partially immune which reduces the risk of them contracting the disease in the future. New bites from infected mosquitoes can help to make people immune again. However, the use of certain vaccines in combination with bednets can undermine that natural immunity. On the one hand, a bednet provides protection, but on the other hand it can cause natural protection to decrease.
The scientists want to emphasise that any research into malaria vaccines is valuable because it provides important insights into the complex way in which immunity to malaria works. It is precisely this complexity that makes it so difficult to develop a malaria vaccine.
Yael Artzy-Randrup, Andrew P. Dobson and Mercedes Pascual: Synergistic and antagonistic interactions between bednets and vaccines in the control of malaria. PNAS Early Edition (21 January 2015).