Every year, malaria kills more than 400,000 people, most of them children. There’s been significant progress against the disease in the past few decades — death rates have fallen nearly in half — but there’s a long way to go. One child dies of malaria every two minutes.

Now, for the first time, we might have a vaccine.

The World Health Organization announced Tuesday that Malawi is rolling out a pilot program of the world’s first malaria vaccine. The vaccine, called RTS,S, will be available to everyone under the age of 2. After the rollout in Malawi, vaccination will begin in Ghana and Kenya later this year. In total, 360,000 children will get the vaccine annually.

In clinical trials, the vaccine prevented about 40 percent of cases of malaria — and only 30 percent of the most severe cases. That’s much, much lower than the success rate of vaccines for most other early childhood diseases — the measles vaccine, by comparison, is 97 percent effective, and the chickenpox vaccine prevents 85 percent of cases and nearly 100 percent of severe cases.

Nonetheless, this is a huge step forward. Malaria is a mosquito-borne disease that causes a fever and chills, and in severe cases anemia, seizures, and respiratory problems. Even preventing 40 percent of cases saves many lives, and since part of the malaria parasite’s life cycle is inside a human host, disrupting some cases will benefit even the people who are not conferred immunity.

We’ve been working for 30 years to find a malaria vaccine. While widespread use of insecticide-treated bednets, preventive treatment, and indoor spraying have driven malaria deaths down significantly, the gains from those approaches have been flattening in recent years. Continued progress against malaria is going to require new tools in the toolbox — and this vaccine looks like an incredibly promising one.

Why a malaria vaccine was such a challenge

Developing a malaria vaccine — even one with only moderate effectiveness — has been a huge challenge. With many viruses, getting the virus once confers lifelong immunity or at least immunity for many years.

Malaria isn’t a virus. It’s caused by a parasite, and having been exposed does not confer lifelong immunity (though it does, like the new vaccine, reduce the odds you’ll get malaria again). The parasite is genetically complex compared to a virus, with thousands of potential antigens researchers have tried to study.

Furthermore, per the Centers for Disease Control and Prevention, malaria vaccine efforts have been hindered by the “lack of a traditional market” — the poorest areas in the world are those hit hardest by malaria, so pharmaceutical companies didn’t see as much avenue to make money. Much vaccine research has been funded by philanthropists, the WHO, and national governments.

That didn’t deter all research, though. There are dozens of potential malaria vaccines under development. In 2015, The Lancet published the results of a large-scale clinical trial of RTS,S. The vaccine was delivered in three doses to infants with a booster shot at age 2.

The results — 40 percent of malaria cases prevented, including 30 percent of severe cases and 60 percent of cases of severe malaria anemia — were a little disappointing at the time to some observers, who had hoped that RTS,S would be even more effective. But they were sufficient to suggest that RTS,S should be deployed at large scale for, as the study authors put it, “an additional means for malaria control whilst the next generation of malaria vaccines are being developed.”

The next generation of malaria vaccines will hopefully be even better. But in the meantime, RTS,S might be sufficient to halt the recent stagnation in progress against malaria.

Malaria cases were declining. Then the decline slowed.

For a long time, we were making impressive progress in fighting malaria. Historically, malaria affected the whole world — it was once a leading killer in the United States, as prevalent here as it is today in Malawi. Eradication efforts in much of the world were a success, but half of the world’s population remains at risk today.

Malaria deaths have continued to fall up to the present day, from more than 800,000 in the year 2000 to 430,000 in 2015. A 2015 study estimating what drove the decrease found that of the 663 million cases of malaria averted in Africa between 2000 and 2015, 68 percent were averted by distribution of insecticide-treated bednets, 19 percent by artemisinin-based combination therapy, and 13 percent by indoor residual spraying.

We continue to use all those tools. But in the past few years, public health experts have started to warn that progress against malaria might be slowing. The WHO has found that artemisinin resistance is growing more common, with artemisinin-resistant parasites detected in five countries in East Asia.

Climate change is expanding the range of malaria-carrying mosquitoes, putting populations at risk that haven’t previously been exposed.

“After more than 15 years of steady progress against the disease,” Bill Gates wrote last week, “the improvement is slowing down. Funding for malaria has also flatlined. If we simply stick with the same tools and the same strategies, progress will stall, and the disease might make a comeback.”

That’s why it’s exciting to hear that a new tool will be available in the fight against malaria. Ten countries expressed interest when the WHO solicited partners for the vaccine pilot, and if the program goes well in Malawi, Ghana, and Kenya, it will certainly be adopted elsewhere.

“We have seen tremendous gains from bed nets and other measures to control malaria in the last 15 years, but progress has stalled and even reversed in some areas. We need new solutions to get the malaria response back on track, and this vaccine gives us a promising tool to get there,” WHO Director General Dr. Tedros Adhanom Ghebreyesus said in a press release announcing the project. “The malaria vaccine has the potential to save tens of thousands of children’s lives.”

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