In July, Kenya will become the third country to join a groundbreaking pilot program to vaccinate the population against malaria, after Malawi and Ghana started immunizing children under 2 with the new vaccine several weeks ago.

The new malaria shot is Glaxo-Smith-Klein’s RTS,S, and it's a big breakthrough for treating the mosquito-borne disease, which kills almost half a million people every year. Researchers have been trying to develop an effective vaccine for more than 60 years, but this is the first one approved and being used to immunize the general public.

The search for a vaccine has been complicated by the fact that malaria is caused by a parasite rather than a virus or bacteria. Parasites change shape throughout their lives and take on different forms in different parts of the host’s body, which makes them extremely difficult to target.

The RTS,S marks the first parasitic vaccine of any kind on the market.

Dr. Ashley Birkett, director of the nonprofit PATH Malaria Vaccine Initiative that supported the development of RTS,S, said the pilot program is “momentous, not only in the case of malaria but also in the potential to fight parasitic diseases.”

But there are some caveats.

The drug has proven to be about 40 percent effective. By comparison, most widely used childhood vaccines have about 85 to 95 percent efficacy. It also needs four doses to work. Still, it’s a welcome addition for health practitioners who’ve recently experienced an increase in malaria transmission in low-income countries.

Between 2000 and 2013, mortality from the disease fell by 47 percent. By 2015, progress in fighting malaria had stalled and in 2017, the World Health Organization reported a significant increase in cases in the ten hardest-hit countries in Africa. As the parasite becomes more resistant to available treatments, any new method of addressing the disease beyond tried-and-tested nets and insecticides, is good news:

“The impact of reducing malaria by 40 percent is huge. We estimate that the addition of this vaccine could result in tens of thousands of lives being saved,” said Dr. Mary Hamel, who’s leading the World Health Organization’s vaccine implementation program.

This segment originally aired June 13, 2019, on VICE News Tonight on HBO.