► What vaccines are available against malaria?
In October 2021, the World Health Organization (WHO) recommended the deployment of Mosquirix, also known as “RTS,S”. This vaccine, developed by the British GSK, had been tested since 2019 in Malawi, Ghana and Kenya. In the field, the vaccination campaign remains limited for the moment by a lack of doses, the need to perform four injections in the first months of the child, and infrastructure problems.
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Another vaccine, similar to Mosquirix, is in phase 2 clinical trials, R21. Developed by the University of Oxford, it is being tested in Burkina Faso and soon in Kenya and Thailand. “A good malaria vaccine must obviously be effective, inexpensive and easy to deploy in the field,” believes Benoit Gamain, malaria specialist at Inserm.
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He himself is working on a vaccine candidate against malaria in pregnant women which should enter phase 2 clinical trials in 2023. “We see that the parasite responsible for the disease develops resistance to each new drug, so vaccines are the only long-term solution to stem the epidemic,” he continues. Still, it is complicated to develop an effective product. Malaria is caused by a parasite, more complex than a virus, with more proteins and potential targets. The research that led to the Mosquirix, for example, dates back to 1987. It therefore took more than thirty years!
► Is the Mosquirix vaccine effective?
This was the big surprise when the WHO gave the green light: the Mosquirix vaccine would only protect up to 30% against serious cases. Far from complete efficiency, then. “It is a first-generation vaccine that must be combined with the means of prevention, such as insecticide-treated mosquito netsrecognizes Benoit Gamain. But it is currently the only vaccine available, and it saves lives. »
A “better than nothing” which worries the actors in the field. “If we vaccinate a child with this product and he still dies, how do we convince the mother to come back for the other children? », says a volunteer in Malawi. The R21 vaccine candidate seems more promising, with an efficiency around 70%, according to interim results published in The Lancetin May 2021. But these good results have yet to be proven in the field.
► What are the other avenues for vaccines against malaria?
Broadly speaking, three types of vaccines are possible against malaria, depending on the stage of the disease at which one intervenes. Mosquirix, the only one currently available, works to block the parasite from infecting the liver, the first step in the cycle.
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It is also possible to block the disease at the blood stage, ie either the entry of the parasite into the red blood cells, or the “hooking” of the parasitized red blood cells to the host receptors. Vaccine candidates of this type would then prevent the severe forms, but not the infection. Finally, it is also possible to block transmission from humans to mosquitoes, to break the cycle and slow down the circulation of the disease.
The search for new vaccines, more effective or easier to use, is essential. In 2020, nearly half of the world’s population was at risk of contracting malaria, and 627,000 deaths worldwide were due to the disease, according to the WHO. Sub-Saharan Africa is particularly affected, recording 93% of deaths.