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Malaria is one of those diseases that's been around for so long that you'd think we'd have figured out how to deal with it by now. And yet, it still kills almost half a million people every year — and most of those people are kids.

One of the main reasons it's still so deadly is that scientists have struggled to create an effective vaccine for it. But last week, the World Health Organization announced that a malaria vaccine has finally made it over all the regulatory hurdles, and is now being given out in the African country of Malawi. And it'll be rolled out in Kenya and Ghana as well later this year.

For this pilot program, the vaccine will be available to children under the age of two and will hopefully reach 360,000 kids a year across the three countries. And though it isn't going to eradicate the disease overnight, if all goes well, this vaccine could become one of the most important weapons in the war against malaria one that might actually give us a fighting chance. You see, we've never had a malaria vaccine good enough to be implemented before.

This one, known as RTS,S, has been in the works for 30 years. It's simply taken that long to develop the vaccine, get it working in animal models, test it for safety and effectiveness in people, and then to make the big decision to start piloting it. And here's the thing: this vaccine isn't that amazing, either.

In clinical trials, it was only about 40% effective, which is way, way less than, say, the MMR vaccine for measles, which works in 93% of cases after just one dose, and 97% after two. The low effectiveness was a disappointment to many scientists when it was first published, and it's not the only drawback to this particular vaccine. To get that 40% protection, kids have to have three doses plus a booster.

That's a lot of shots, which means it's harder to ensure kids get through the whole vaccination process. Also, it works best in kids 5 to 17 months old. For younger infants, it was less effective.

But health experts are still pretty excited about moving forward with it, because they believe that it has the potential to save tens of thousands of children's lives. And to be honest, it's the best we've got. Because it's been really, really challenging to make a malaria vaccine that works at all.

There's a few reasons for that. One of them is that it's not a lucrative market for pharmaceutical companies, since malaria disproportionately affects poorer parts of the world. It's kind of lousy, but there you have it.

And those who have dedicated the time and resources have come up against wall after wall. Like, right off the bat there's a challenge, because actually, like, getting malaria doesn't confer lifelong immunity, like with some other diseases. That's not a good sign when you're trying to come up with a vaccine for something, since vaccines work by essentially triggering a person's natural immunity without them having to live through the disease.

Most vaccines expose people to small, harmless amounts of whatever causes the disease so that their immune system can learn to recognize it and build up antibodies. Those are y-shaped immune proteins which bind tightly to things, flagging them for destruction by your immune system. And if your body has these antibodies against a particular pathogen, it can deploy them rapidly in the face of a future infection.

But malaria can subvert this defense mechanism. And that's in part because it's not caused by a virus or bacteria. Instead, it's caused by several species of parasites from the genus Plasmodium.

And while they are single cells, they're way more complex genetically than your average pathogen. Not only are there multiple species—within a given species, there can be multiple phenotypes. Exactly what they look like can vary from individual to individual, which makes it that much harder for the immune system to find them reliably.

And they have this complicated life cycle that takes place in both the mosquito and in different parts of the human body. Humans get infected when they're bitten by a mosquito that's carrying the parasites. These then make themselves at home in the liver for a while to grow and reproduce.

They can stay dormant for weeks or years there before making their way into red blood cells. That's where they multiply again by a slightly different mechanism, which kills the red blood cells in the process. This is the phase of malaria that causes all the symptoms, and that can be lethal.

And the parasites look different during all these different stages—there's no single antibody that binds to them all. Basically, there's a lot going on, and that makes it hard to decide what to train the immune system to respond to. So a malaria vaccine is a pretty big ask—which is why RTS,S is so exciting.

It protects specifically against the species which causes the deadliest form of malaria. And it does that by helping the body develop antibodies against a protein called circumsporozoite or CS protein. It's a protein the parasite secretes during that first stage of malaria, when the parasites infect the liver, because it helps them get inside of liver cells.

Part of the reason that the vaccine is only 40% effective is because it targets a particular version or allele of the CS protein. It's slightly more effective against parasites with that allele, and slightly less effective against parasites that have other versions. What's cool about targeting this stage of the disease is that if the parasites don't take up residence in the liver, they can't go on to infect the bloodstream and cause symptoms.

But it's not necessarily the only stage or the only protein that makes sense to target. In fact, scientists have argued that the CS protein might not be the best choice— it might not play an important role in the gradual acquisition of natural immunity that some people get after having malaria multiple times, for example. And in the end, combining this vaccine with vaccines that act on other parts of the parasites' life cycle might someday be the most effective way to combat infections.

In the meantime, doctors are working with what they've got. Right now, malaria kills a child every two minutes… and that awful stat is actually a big improvement over the damage it used to inflict. Many lives are already saved by preventative measures like bed nets sprayed with bug repellents, preventative medication dolled out during the mosquito season, and the use of insecticides in homes.

Having one more weapon against the parasites, no matter how imperfect, could make a big difference. If the pilot programs in Malawi, Kenya, and Ghana do reduce deaths, the vaccine could become a more permanent part of many countries' health programs. And it could help stimulate funding for further vaccine development.

This may not be the malaria vaccine to end all malaria vaccines, but it could be exactly what we need to tide us over while a more effective eradication strategy is developed. Thanks for watching this episode of SciShow News! And a special thank you to all of our channel members.

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