The world’s first mass vaccination program against malaria, announced this week, aims to prevent millions of children from getting malaria and thousands dying from the debilitating disease.
The World Health Organization (WHO) has recommended the widespread use of the RTS,S/AS01 (Mosquirix) vaccine in young children, who are most at risk of malaria in Africa.
Malaria is a big deal
Mosquitoes transmit the Plasmodium falciparum parasite from person to person when they bite. So until now, our fight against malaria has consisted of using mosquito nets to avoid being bitten and spraying insecticides to kill mosquitoes. Then there are medicines to prevent or treat a malaria infection.
However, the parasite has developed resistance to antimalarial drugs, and mosquitoes have developed resistance to insecticides. Nevertheless, the existing control measures since 2000 have led to a significant reduction in malaria deaths.
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 cases of malaria.
So we need additional tools like an effective malaria vaccine if we want to control the disease globally.
WHO’s recommendation that Mosquirix vaccine be introduced in children at high risk of infection with P. falciparum, which is widespread in Africa, is an important step in the fight against the deadliest human malaria parasite.
Read more: How our red blood cells are evolving to fight malaria
What did the WHO recommend?
The WHO recommended four doses of the vaccine in children aged five months and older.
This recommendation follows recent results from a pilot program in Ghana, Kenya and Malawi that has vaccinated 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 (to over 90%) who have access to at least one malaria prevention intervention.
The vaccine has a good safety profile, reducing cases of clinical and severe malaria, which can be fatal.
Read more: New malaria vaccine proves highly effective – and COVID shows how quickly it could be deployed
What do we know about the vaccine?
Mosquirix is a “subunit” vaccine. That means it only contains a small part of the malaria pathogen, which is made as a synthetic protein.
This protein is coupled with an “adjuvant,” a molecule designed to stimulate a powerful immune response.
The vaccine works mainly by stimulating the body to produce antibodies against the parasite, neutralizing it and preventing it from entering liver cells. These are the first cells the parasite invades when it enters the body.
The vaccine also works by helping to trigger an inflammatory response when another part of the immune system is reacting.
READ ALSO: Male Mosquitoes Don’t Want Your Blood But Still Find You Very Attractive
The vaccine is not perfect
The level of protection offered by the vaccine is not ideal. Protection varies with the age of the child at vaccination, with lower protection for young children compared to older children. In the older children (5-17 months old) 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 regular booster doses are required. Alternative vaccination schedules are also being evaluated.
Still, the vaccine can make a significant contribution to malaria control when used in high-risk areas and with other control measures.
A model study estimated that Mosquirix could prevent up to 5.2 million cases of malaria and 27,000 infant deaths in sub-Saharan Africa each year.
Why did it take so long to get here?
Developing a malaria vaccine is a challenge. Technically, it is difficult to develop a vaccine against a parasite that lives in two hosts (mosquitoes and humans).
There has also been limited interest from pharmaceutical companies in developing a malaria vaccine.
Although travelers would benefit from a vaccine when traveling to affected countries, the people 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 developed through a partnership between GlaxoSmithKline (GSK) and the Walter Reed Army Institute of Research in the USA.
This time frame is not long considering that both the antigen design and the adjuvant system were novel.
The Bill & Melinda Gates Foundation and GSK supported further development, including evaluation of the vaccine in clinical trials. Over three decades, they invested around $700 million in developing the vaccine.
This current version of Mosquirix will probably not be the last. Preliminary results for a new modified vaccine called R21 are encouraging.
Other malaria vaccines in development include whole parasite vaccines. These use the entire malaria parasite that has been killed or modified so that it cannot cause a malaria infection but can still stimulate an immune response.
Passive vaccines are also being studied. Long-lasting antibodies are injected to prevent malaria infection.
Read more: COVID-19 isn’t the only infectious disease scientists are trying to find a vaccine for. Here are 3 more
A whole new set of challenges
In the meantime, the WHO recommendation presents a number of new challenges.
Malaria-affected countries must decide whether to include Mosquirix in their national malaria control strategy.
Crucial funding decisions by the global public health community are required to enable widespread vaccine uptake among the children who will benefit most.
Production capacity for tens of millions of doses per year, global supply chains for vaccines and a distribution infrastructure in malaria-affected countries are also required.
Finally, each country must maximize uptake of the vaccine and ensure the four-dose vaccination schedule is complete in order to reap the full benefits of the vaccine.
Correction: This article originally stated that the Bill & Melinda Gates Foundation and GSK invested approximately $700,000 million to support vaccine development instead of $700 million.