A first vaccine to relaunch the fight against malaria

It is not perfect, but a first vaccine against malaria has just been recommended by the WHO. RTS, S is a hope. What relaunch the fight against a hard parasite to fight and treat.

The World Health Organization (WHO) has announced a historic measure: it has recommended large-scale use of the first vaccine against malaria (or malaria), RTS, S. This recommendation is based on the results of a pilot program ongoing in Malawi, Ghana and Kenya. Malaria is a huge global health challenge, with an estimated 409 people dying from it in 000 alone. The WHO African region bears a significant share of the burden of malaria - with 94 % of all malaria cases and deaths. Children under five are the most vulnerable. Ina Skosana asked medical entomologist Eunice Anyango Owino to explain this development and its significance.

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It took 30 years to create this vaccine: why?

The main reason is that the parasites of the malaria, of the kind plasmodium (falciparum, etc.), has a very complex development. It actually passes by different stages, some appearing in the mosquito (which transmits it) and others in humans. Scientists have therefore had to adopt various approaches.

In humans, there are two phases. These are the following:

• The pre-erythrocytic stage (without symptoms). This is the period during which the parasite, received after a mosquito bite, enters the bloodstream and reaches the liver. It enters and will multiply there, after which it is again released into the blood.
• The blood stage. It corresponds to the sequence in which the numerous parasites released by the liver enter red blood cells (blood cells responsible in particular for transporting oxygen) and multiply there. The blood cells are destroyed en masse, which causes symptoms associated with this disease, in turn releasing new parasites, which will be able to invade other cells, etc.

An effective vaccine against the first stage (pre-erythrocytic stage) would be able to elicit an immune response preventing infection of liver cells or would cause destruction of infected liver cells. The RTS, S vaccine, which targets the parasite falciparum, responsible for the most serious forms, is of this type.

An effective vaccine for the second stage (blood stage) would have three possible modes of action: elicit immune responses preventing infection of red blood cells; decrease the number of parasites in the blood; reduce the severity of the disease by allowing the body to develop natural immunity with a low risk of becoming ill.

A final option would be to block transmission: vaccinated people would generate antibodies that would be able to block the maturation of parasites in mosquitoes carrying the disease that would bite them to feed.

Another factor that has contributed to this delay is that scientists working on possible vaccines against malaria have long struggled to understand the specific immune responses associated with protection against the parasite.

This is partly due to the fact that the parasites that cause malaria - Plasmodium falciparum for the best known - display such a variety of elements capable of eliciting an immune reaction on their surface (antigens) that it helps them evade our defenses and makes vaccines based on a few specific antigens less effective.

What do we know about this vaccine?

The RTS, S vaccine (trade name Mosquirx) is given in four doses to children aged 5 to 17 months; the first three doses are given every month, the fourth, a booster dose, is given between 15 and 18 months.

THEefficiency is about 40% against the development of malaria and 30% against severe forms.

Each disease - and vaccine - has a specific mode of action. WHO has set a target efficacy level of 50% and above for most vaccines, and the most effective exceed a protection level of 75%; Covid-19 vaccines based on messenger RNA technology from Pfizer and Moderna offer a level of protection of 90%. (It is therefore one of the vaccines recommended by the WHO with the lowest efficacy ... But due to the difficulty of developing treatments (and the resistance that appears), it has a strong interest for the countries with the lowest efficacy. most affected by malaria. editor's note)

What are the next steps ?

First, WHO and the manufacturers of the vaccine, GlaxoSmithKline, will push countries, especially those with high malaria, to adopt the vaccine as part of their national malaria strategies.

They will also ask these countries to put funds aside.

They will also participate in fundraising from the global health community or work with partners, for a wider deployment of the vaccine.

There should be equitable and long-term access to the vaccine. The vaccine must also be cost effective.

The hope is also that this WHO announcement will restart the race to find even more effective vaccines against malaria. The reports reports from the Jenner Institute at Oxford University suggest that a malaria vaccine meeting the WHO target of 75% is being tested in Burkina Faso.

What interest in the fight against malaria in Africa?

This vaccine is an additional tool in the malaria control and control toolbox.

Granted, it does not provide complete protection. But it will be introduced in a set of other tools aimed at reducing infections and lowering the number of deaths. Other measures include mosquito nets and indoor insecticide sprays.

It also has great potential in heavily affected areas in sub-Saharan Africa, especially if used in combination with pre-existing malaria prevention methods. For example, a London School of Tropical Medicine study reported a 70% reduction hospitalizations and deaths in children who received RTS, S (Mosquirx) vaccine and antimalarial drugs.

The fight against malaria has recently stalled in some African countries, and countries like Sudan and Eritrea have even experienced a significant upsurge.

This vaccine, even imperfect, will give new impetus to this major health fight. And he offers the promise to get him back on track.

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Eunice Anyango Owino, Medical entomologist at the School of Biological Sciences, University of Nairobi

This article is republished from The Conversation under Creative Commons license. Read theoriginal article.