Eight things to know about the RST, S malaria vaccine

A child receives the malaria vaccine in Ndhiwa, Kenya, on September 13, 2019, as part of the pilot program deployed by the World Health Organization.

© Brian Ongoro / AFP

Text by: Anoushka Notaras

7 mins

Malaria is a thousand-year-old infectious disease which still represents a major public health problem today, affecting more than 200 million people worldwide and causing more than 400,000 deaths per year, the vast majority of them in Africa.

While we have been able to produce several vaccines against the Covid-19 virus in less than two years, the research for an antimalarial vaccine has been going on for several decades.

The WHO recommendation of 6 October 2021 for the massive deployment of the RTS, S vaccine in children in Africa was therefore described as “ 

 ” by its director general, Tedros Ghebreyesus.

What is this vaccine?

To what extent does it help the fight against malaria? 

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What is the RST, S vaccine? 

Malaria is a potentially fatal parasitic disease transmitted to humans by the bites of infected female mosquitoes of the Anopheles genus that causes fever, headache, followed by cycles of chills, fever and sweat. According to the World Health Organization (WHO), malaria affected 229 million people in 2019, including 94% in sub-Saharan Africa, claiming 409,000 victims, including 267,000 children under 5, representing 67 % of deaths.  

The Mosquirix vaccine, or RTS, S / AS01 (RTS, S), was thus developed for children aged 17 months to 5 years and requires four doses to be fully protected.

Designed in 1987 by the British pharmaceutical giant GlaxoSmithKline (GSK) in collaboration with the NGO Path and the Gates Foundation, it targets 

, the most frequent and dangerous parasite of the five species of parasites responsible for malaria, which is mainly widespread in sub-Saharan Africa.  

How effective is it? 

The RTS, S vaccine was the subject of a first clinical trial on 15,000 young children from 2009 to 2014 in seven countries in sub-Saharan Africa. This study demonstrated a vaccine protection rate of 39% and 29% for severe forms of the disease over four years. In 2015, WHO requested the establishment of a large-scale pilot program in three countries of sub-Saharan Africa: Ghana, Kenya and Malawi. Launched in 2019 for a period of four years, its objective is to immunize 360,000 children per year in the three countries. In 2021, the 2.3 million vaccines administered helped protect 40% of children and reduce cases of severe forms by 30%. According to the WHO, the vaccine would also reduce the need for blood transfusion by 29% to treat anemia due to malaria. What's more, 

 in Mali and Burkina Faso, published by 

, report that combining antimalarial treatment with the vaccine would reduce malaria cases by more than 75% in young people children. 

Why are children more affected than adults

In endemic areas, children are protected from malaria during their first weeks of life thanks to their mother's antibodies. It is between the age of

 they are most vulnerable, especially to severe forms of malaria, because their body has not yet acquired what is called premunition immunity. . This specific immunity protects a person who has already been infected from superinfection. It is acquired gradually after repeated exposure to the parasite, persists as long as one is exposed to it, but stops when one is no longer exposed. It partly explains the better resistance of adults living in endemic areas when the immune system of young children has not yet had time to do this "learning".  

Pregnant women are also very vulnerable: pregnancy reduces their immunity to malaria infection which can lead to severe anemia, with serious consequences for the unborn child such as delayed fetal growth or the risk of malaria. 'premature delivery. 

Does this vaccine have any side effects

Overall, the vaccine is generally well tolerated.

Phase 3 clinical trials have shown reactions similar to other vaccines, such as pain and swelling at the injection site and fever.

Cases of seizures have been reported in the week following the injection, but remain without sequelae.

A few cases of meningitis have also been reported.

In 2015, the European Medicines Agency issued a positive opinion, judging that the benefits of the vaccine outweighed the risks.  

Does this vaccine replace existing treatments? 

No.

It is an additional tool in the fight against malaria that is in addition to all 

 such as insecticide-treated mosquito nets, antimalarial treatments, the rapid diagnostic test (TRD), symptomatic treatments and patient follow-up. 

Why did it take so long to develop it? 

The majority of vaccines produced in the world target viruses and bacteria, " 

 ", explains Sandrine Houzé, professor of parasitology at the University's faculty of pharmacy. from Paris.

the 

 is a complex organism with more than 5,000 genes, while in comparison, the virus responsible for Covid-19 has only about 20.

Sophisticated and protean, its life cycle and the form it takes depend on the host (human being or mosquito) and the organ (liver or red blood cells) it has infected.

This dynamism has allowed it throughout human history to challenge immunity by making multiple mutations, causing constant questioning of research into new solutions.

The RTS, S vaccine precisely targets the parasite in its initial form, between the bite of the mosquito and its arrival in the liver.

It is this characteristic which explains in particular its limited rate of protection.  

How is the deployment of this vaccine financed? 

The pilot program received an initial funding of US $ 15 million from the Global Fund to Fight AIDS, Tuberculosis and Malaria in 2016. In August 2021, the Global Fund, Gavi, the Vaccine Alliance and the UK company MedAccess awarded it an additional $ 70 million to ensure the continuity of production of the vaccine.

For its part, GSK, which has invested nearly $ 700 million in vaccine research, donated 10 million doses.

The Gavi Vaccine Alliance and the various financial actors must now assess the financing of the massive deployment of the vaccine in sub-Saharan Africa recommended by the WHO.  

Are other vaccines under study? 

Among the thirty vaccine candidates under study, R21 / Matrix-M, a vaccine developed for more than ten years by the University of Oxford and the Institute for Research in Health Sciences (IRSS) in Burkina Faso Faso, revives hope. Phase 2 clinical trials conducted in 2019 in Burkina Faso on a group of 450 children aged 5 to 17 months reported a protection rate of 77%, above the 75% requested by the WHO. “ 

[…]

to the upcoming

Said Halidou Tinto, professor of parasitology, regional director of the IRSS in Nanoro, and principal investigator of the trial.  

In July 2021, the German laboratory BioNTech, which created the Pfizer vaccine against Covid-19, announced that it was embarking on a program to develop a messenger RNA vaccine to fight malaria.

Work is due to start at the end of 2022.   

Our selection on the subject:

• To read :

→ Malaria vaccine: three infectious disease specialists comment on the WHO announcement

→ Malaria in Africa: how to prevent drug resistance?

→ DRC: the malaria epidemic progressed in 2020 due to Covid-19 

→ Malaria: Anopheles stephensi, the mosquito from Asia that threatens Africa

• To listen :

→ How to avoid a resurgence of malaria in sub-Saharan Africa?

→ Gabon: in the footsteps of mosquito hunters in Lambaréné

→ Very worrying upsurge in malaria cases in Madagascar

→ Malaria: a GMO mosquito fungus

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