The world’s first mass immunization program against malaria, announced this week, is set to prevent millions of children from contracting malaria and thousands more from the debilitating disease.
The World Health Organization (WHO) has recommended widespread use of the RTS, S/AS01 (Mosquirix) vaccine in young children who are at highest risk of malaria in Africa.
Malaria is a big deal
mosquitoes spread parasites Plasmodium falciparum from person to person when they bite. So until now, our fight against malaria has included using mosquito nets to avoid biting mosquitoes and spraying insecticides to kill mosquitoes. Then there are drugs to prevent or treat malaria infection.
However, the parasite has developed resistance to anti-malarial drugs and mosquitoes have developed resistance to insecticides. Yet existing control measures have resulted in a significant reduction in the number of malaria deaths since 2000.
In recent years, however, progress has stalled. In 2019, malaria infection resulted in 409,000 deaths worldwide, mostly in children under the age of five, and 229 million new malaria cases.
So if we want to control this disease globally we need additional tools, such as an effective malaria vaccine.
WHO recommendation to implement mosquito vaccine for children at high risk of infection P. falciparum, which is widespread in Africa, is an important step towards controlling the deadliest of human malaria parasites.
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What did WHO recommend?
The WHO recommends four doses of the vaccine in children aged five months.
The recommendation follows recent results from a pilot program in Ghana, Kenya and Malawi to vaccinate more than 800,000 children since 2019.
The program demonstrated that delivering the vaccine to high-risk areas is feasible and cost-effective. It also increased the number of children (over 90%) who have access to at least one intervention to prevent malaria.
The vaccine has a good safety profile and reduces cases of clinical and severe malaria, which can be fatal.
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What do we know about the vaccine?
Mosquirix is a “subunit” vaccine. This means that it contains only a small fraction of the malaria parasite, which is produced as a synthetic protein.
This protein is paired with a “helper,” a molecule designed to stimulate a stronger immune response.
The vaccine works primarily by stimulating the body to make antibodies against the parasite, neutralizing it and preventing it from entering liver cells. These are the first cells when the parasite enters the body.
The vaccine also works by helping to mount an inflammatory response, when a different part of the immune system reacts.
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vaccine is not correct
The level of protection provided by vaccines is not ideal. Protection varies with the age of the child at the time of vaccination, with younger infants having less protection than older children. In older children (5-17 months of age), this averaged about 36% protection against the development of clinical malaria over a four-year period.
Protective immunity also declines rapidly over time. This means that regular booster doses will be needed. Alternative vaccination schedules are also being evaluated.
Nevertheless, the vaccine can still make a significant contribution to malaria control when used in areas with high malaria risk and with other control measures.
A modeling study estimated that in sub-Saharan Africa, Mosquirix could prevent 5.2 million cases of malaria each year and 27,000 deaths in young children.
Why did it take so long to get here?
Developing a malaria vaccine is challenging. Technically, it is difficult to develop a vaccine against a parasite that lives in two hosts (mosquitoes and humans).
The interest of pharmaceutical companies in developing a malaria vaccine has also been limited.
Although travelers will benefit from the vaccine when traveling to affected countries, those most in need of a malaria vaccine live in some of the world’s poorest countries. So there is little financial incentive to develop a vaccine.
Mosquirix is the result of more than 30 years of research and was created in the United States through a partnership between GlaxoSmithKline (GSK) and the Walter Reed Army Institute of Research.
This time frame is not long, given that both the antigen design and the adjuvant system were novel.
The Bill & Melinda Gates Foundation and GSK supported further development, including evaluating the vaccine in clinical trials. Over three decades, he invested about US$700,000 million to develop the vaccine.
This current version of Mosquirix is not expected to last. Preliminary results from a newly modified vaccine called R21 are encouraging.
Other malaria vaccines in development include whole parasite vaccines. These use whole malaria parasites that have been killed or altered, so it cannot cause malaria infection but can still stimulate an immune response.
Inactivated vaccines are also being investigated. These include injecting long-lasting antibodies to prevent malaria infection.
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a new set of challenges
Meanwhile, the WHO recommendation presents a new set of challenges.
Malaria affected countries must decide whether to include Mosquirix as part of their national malaria control strategy.
Significant funding decisions will be needed from the global public health community to enable a wider rollout of the vaccine to the children who will benefit most from it.
Countries affected by malaria will also need manufacturing capacity of millions of doses each year, a global vaccine supply chain and distribution infrastructure.
Ultimately, each country will need to make sure to get the most out of the vaccine and meet a four-dose vaccination program to get the most out of the vaccine.