Malaria vaccine that combines parasite with treatment shows promise

By Clare Wilson

A new kind of malaria vaccine involves injecting people with the malaria parasite, then a few days later giving them a medicine that kills the pathogens. The approach has shown promising results in an early-stage trial.

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Malaria, an infectious disease spread by mosquitoes, is one of the world’s biggest public health problems. It is particularly deadly for young children in Africa.

There is already a vaccine available, called Mosquirix, which works by injecting people with a molecule found on the surface of the parasite. But its efficacy wanes over time, falling to about 5 per cent after seven years.

Some groups are working on an improved Mosquirix-like vaccine, which produced positive results in April. But Patrick Duffy at the US National Institutes of Health and his colleagues wondered about an alternative approach: injecting people with the whole parasite, then quickly giving a malaria medicine to stop them becoming ill.

They tried two different antimalarial drugs and different doses of the parasite in a small “human challenge” study, in which people are vaccinated then three months later deliberately exposed to the malaria parasite to see if they develop the illness.

When the antimalarial pyrimethamine and a high vaccine dose of parasite was used, seven out of eight people were protected against getting sick, if the same strain of parasite was used in the vaccine as for the challenge. If a different strain was used – a tougher test – seven out of nine people were protected. Another antimalarial drug called chloroquine protected six out of six people against a different-strain challenge.

These high efficacy figures don’t necessarily mean this approach would work better than Mosquirix in real life. “But it’s a level of protection that hasn’t been seen before [in challenge trials],” says Duffy.

The main drawback of the new strategy is that if people fail to take the antimalarial drug after being vaccinated, they would be likely to develop malaria. To avoid this, a larger trial has begun in Mali in which people are given pyrimethamine at the same time as they are vaccinated.

Journal reference: Nature, DOI: 10.1038/s41586-021-03684-z

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