As climate change persists, new weather systems could allow malaria to spread and thrive more easily, making the malaria vaccine a form of climate resiliency.
In the fall of 2021, as the world was bracing itself for a major wave of yet another variant of the SARS-CoV-2 coronavirus, a medical breakthrough occurred that garnered little attention by comparison.
After 30 plus years of research and development, the World Health Organization (WHO) approved use of the first ever malaria vaccine known as RTS,S or commercially as Mosquirix. And while this may be considered a triumph of modern medicine, it’s also a win for climate resiliency.
The impacts of climate change are not felt equally across the globe — striking developing nations the hardest. Severe heat waves, droughts, and other catastrophic weather events only lessens one’s resilience to disease. Addressing these existing, preventable diseases, therefore, is a climate change issue and can only make a society stronger and more resilient in the face of future potential hardship.
Malaria is a febrile, or feverous, disease caused by the single celled parasite Plasmodium. Several species of Plasmodium can cause illness in humans, but the deadliest is P. falciparum, which is heavily present in Sub-Saharan Africa. The parasites have an extremely complex life cycle and travel between vertebrate hosts through bites of female Anopheles mosquitoes whose range stretches across the Equator from South America to Sub-Saharan Africa and Southeast Asia. Symptoms tend to appear about 10 to 15 days after infection and include intense fever, aches, chills, and vomiting. If left untreated, it can result in severe illness and death within 24 hours.
Malaria is a preventable and curable disease, yet its global impact remains profound and highly inequitable. According to the WHO, there were an estimated 241 million cases in 2020 with 627,000 known deaths. Sub-Saharan Africa was home to 95 percent of these cases and 96 percent of the deaths. About 80 percent of those occurred in children under the age of five.
The Plasmodium parasites that cause malaria have been known for over 130 years, yet a complicated life cycle of many stages has made global eradication of the disease through vaccine development exceptionally challenging. Researchers at the London-based pharmaceutical firm GlaxoSmithKline (GSK), for example, have been developing and testing the RTS,S vaccine since 1987 at a cost of $750 million.
Despite these many years of research, pilot programs in Ghana, Kenya, and Malawi since 2019 have shown the vaccine to be only modestly effective, preventing about 30 percent of severe malaria cases in children under five after a series of four injections.
This has caused disappointment among some health officials. “I don’t think a 30 percent effective vaccine would be acceptable for Americans,” Badara Cisse, a malaria researcher at the Institute for Health Research, Epidemiological Surveillance and Training in Dakar told Nature.
Nevertheless, many other experts still welcome the vaccine as a positive development for combating the disease.
“Look, this is really encouraging,” Jeff Shaman, professor of environmental health sciences at Columbia University, told Currently. “We have been trying for 40 years to get a vaccine for HIV and we’ve still not gotten it. Some of these organisms are very challenging. Covid should not bring about an illusion that it is a simple process every time to rapidly generate a vaccine against something.”
Modeling in one study showed that, if administered to all children in countries with high incidences of P. falciparum, the vaccine could save the lives of 23,000 children a year.
Additionally, researchers from one clinical trial found that the vaccine could be more effective if distributed in tailored rollouts when disease transmission seasonally peaks; childhood malaria deaths decreased 73 percent when children received three doses in the run-up to the rainy season and another dose before the rainy season in the two subsequent years.
Experts promoting the vaccine see it as another useful tool in the toolbox rather than a panacea, and argue that, if used in conjunction with other preventive methods, it could be a major step in the global treatment of malaria.
“This is a historic moment,” said WHO Director-General Dr Tedros Adhanom Ghebreyesus in a public statement late last year.
“The long-awaited malaria vaccine for children is a breakthrough for science, child health and malaria control. Using this vaccine on top of existing tools to prevent malaria could save tens of thousands of young lives each year.”
Malaria used to occur in most parts of the world, but disappeared in wealthier countries with efforts to eradicate Anopheles mosquitoes. Wealthier nations could afford the large-scale mobilizations, or the “boots on the ground entomologists that go out in the field, collect mosquitoes and look at what’s going on,” said Shaman. Learning what habitats they exploited, the ecologies they lived in, and how weather systems affect them “led to the elimination of autochthonous malaria, within North America and the US, certainly,” he explained.
Malaria and Climate
In fact, weather systems are one of the most important factors to consider when tracking the spread of malaria.
“Temperature, humidity, and rainfall,” said Shaman, “those tend to be the three [conditions] you look at a lot,” adding that sometimes researchers focus on land wetness as well.
Some researchers have taken this fact and tried to posit what will happen to the spread of malaria as climate change persists. Many have even wondered if the disease could re-enter places it has been eradicated from –– imagining Anopheles mosquitoes taking over cities like Houston or Atlanta. But this ignores a lot of other environmental and societal factors that also have roles to play in the spread of these malaria vectors.
Shaman noted that in places like Houston, which is by all rights a malaria zone due to its humid climate, people “drained the swamps, they built good housing…they go from an air-conditioned home to an air-conditioned car to an air-conditioned workplace and they don’t encounter mosquitoes enough. And it’s that kind of developed world control that limits it.”
He explained that malaria needs both human and mosquito to survive and without regular interaction between the two, it will go extinct locally. “You have to consider the climate mosquito borne disease question in the larger context of all the things that are in place and that includes the development, the medical and public health resources, the ecology of it, competitors, predators, all this other stuff. You have to consider it holistically,” he said.
But, the fact that malaria is unlikely to move into a place like the United States because of climate change does not mean its range won’t or couldn’t grow. And it does not mean that it couldn’t get worse in the places where it already exists.
Maria Diuk-Wasser, professor and disease ecologist at Columbia University, told Currently that if malaria expands into new territory, it likely will be in specific regions of areas that it already has a foothold in like the highlands of Africa and parts of South America and Southeast Asia, thereby increasing suffering on countries already under its yoke.
What’s more, extreme weather events like flooding — and in a cruel twist even drought — could increase transmission in these places by creating optimum breeding conditions for Anopheles mosquitoes.
“Higher precipitation may enhance conditions for breeding but sometimes drought does as well, as people would use other water sources and sometimes store water,” said Diuk-Wasser. Buckets of stored water create breeding grounds for Anopheles right inside peoples’ homes.
The RTS,S vaccine, then, while only modestly effective, might be another helpful tool for getting underfunded diseases like malaria under control. Regardless of its drawbacks, if used in conjunction with other preventable methods, like antimalarial drugs and insecticide treated bed nets, it can only strengthen community health in a way that makes societies more resilient in the face of future climate-induced privation.
“The truth is,” said Shaman, “there’s going to be winners and losers with [climate change]. Wealthier entities are going to be able to buffer themselves from the consequences of climate change to a greater degree than those without the resources. And it’s going to be marginalized populations and countries that don’t have the resources that are going to feel the effects of climate change more fully because they’re not going to be able to compensate or adapt to it.”
Vaccine research and development is one push on the scales at tipping this imbalance.