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Can the development of vaccines against malaria allow Africa to eliminate the disease by 2030 as it has set itself the objective? In August, Unicef announced a contract described as“historical” with the purchase of 18 million doses of the first antimalarial vaccine, Mosquirix (RTS, S/AS01), for an amount of 177 million dollars (170 million euros) in order to accelerate the fight against this particularly tropical disease fatal to children.
In total, more than a million of them have already received one to four doses, reported the World Health Organization (WHO), which officially recommends it, despite an effectiveness limited to around 30% over time. Experts estimate that, deployed on a large scale, Mosquirix could save the lives of 40,000 to 80,000 children each year.
” Although this major step forward is to be celebrated, vshe vaccine is not yet the miracle solution we expect, explains the Congolese Francine Ntoumi, epidemiologist and coordinator of the Central African Network on Tuberculosis, HIV and Malaria (Cantam). Because of its poor long-term effectiveness, mothers will have to keep their children sleeping under a mosquito net, by far the most effective tool to date. » The RTS, S is therefore added to the arsenal of the fight alongside the impregnated mosquito net, insecticides, rapid tests and drugs.
Hopes are also pinned on a second serum currently being tested, R21/Matrix-M, designed by Oxford University. The first, very promising phase II results, published in September in the journal Lancet Infectious Diseases, demonstrated an efficiency oscillating between 70% and 80%. While the vaccine is currently in phase III testing, the British institution is already aiming for mass production from 2023.
“There is still a long way to go, warns Didier Ménard, professor of parasitology at the University of Strasbourg and director of the genetic unit of malaria and resistance at the Institut Pasteur in Paris. For now, it has only been tested in Burkina Faso, which does not mean that it will be effective in the DRC. There are many different strains within the species of plasmodia. We have not yet found a universal vaccine for all of Africa. »
However, there is urgency. Because the continent almost alone bears the burden of malaria with 98% of cases in the world and 96% of deaths. In 2020, 241 million people were infected and 627,000 people died, 80% of them children under the age of 5, according to the latest WHO figures. And after twenty years of progress, the fight against contamination is stagnating and mortality has even experienced a rebound of 12% compared to 2019.
Blame it first on Covid-19, which has destabilized health systems, slowed the production of antimalarial drugs and captured part of the financial resources allocated until then to “great killers” such as HIV, tuberculosis and malaria.
But other reasons threaten the progress made so far. As the resistance to insecticides developed by the Anopheles mosquito, host of the parasite Plasmodium falciparum which it transmits to humans by bite. That of the parasite itself to antimalarials based on artemisinin, a key molecule in treatment. Or the mutation of the parasite antigen, tracked by rapid tests, which produces many false negatives. A major pitfall if we want to avoid blind treatment and reinforce antimicrobial resistance.
The spread since 2012, via the east of the continent, of a species of mosquito (Anopheles stephensi) came from Asia, carrier of the two most dangerous strains of plasmodia for the human body (falciparum and vivax) and already resistant to several classes of insecticides, worries the WHO and researchers.
The coronavirus pandemic however, had the unexpected effect of stimulating “the development of African laboratories, their research and diagnostic capacities”, positive Didier Menard. Malaria case-finding has also seen a surge across most of the continent, says the Global Fund 2022 report published in September, and is now between 73% and 100%.
The populations have also been made aware of the concept of asymptomatic carriers. Because, as with Covid-19, the overwhelming majority of adults have developed some degree of immunity and are unaware that it carries the parasite. A very useful awareness campaign for the future of prevention, because “we will have to tackle this huge reservoir of transmitters, further analyzes the scientist. This can be through mass drug treatment strategies. The acceptability of the populations will be crucial”.
Still, the top priority is to find an alternative to artemisinin, currently the only molecule available, as quickly as possible. On the research front, scientists are not to be outdone. About twenty drugs are under development.
And new avenues are explored. Serotherapy, for example, which consists of directly injecting monoclonal antibodies just at the start of the transmission season. A method tested in Mali and which revealed 88% effectiveness at six months. Or epigenetics, which consists of killing parasites in the blood, including those resistant to artemisinin, by neutralizing the genome responsible for its adaptation during its passage through the human body. And again the technology of messenger RNA applied to the development of a future vaccine.
So many projects requiring resources that will increase. While the seventh replenishment conference of the Global Fund, which finances nearly two-thirds of the fight against malaria, opened in February with the hope of raising 18 billion dollars, it ended in mid-November with $15.7 billion in pledges. An inflection compared to the previous replenishment of the Fund in 2019, which had exceeded the expected target of 14 billion dollars. Admittedly, the pledges are larger, but part of this windfall ($4.4 billion) had been urgently allocated to the response to Covid-19, a system that the Global Fund has extended until 2025.
North and South, “the resources of money are not unlimited and we must constantly arbitrate so that they are distributed on the right priorities”, explains Pascal Ringwald, a malaria specialist who has co-chaired the United Nations program since April. If there is still an imbalance in funding, which is reflected in the malaria incidence curve, continues the UN official, the continent also suffers from numerous conflicts, instability, considerable population displacements which have a severe impact on the fight against major diseases. »
On the financing side, “We won’t know until 2023 if we’ve really gotten out of the zone of turbulence, adds Francine Ntoumi, from Cantam. It is always much faster to obtain research credits for Covid than for tropical diseases. But we cannot make donors feel guilty if our States do not respect their own commitments to invest more in health. Let’s do better with what we already have and we will save many more lives. »
Article produced as part of a partnership with Africa Santé Expo, which will take place from 1er to December 3, 2022 in Abidjan.
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