SIAYA, Kenya—A mother watched with dread as a nurse inserted a tube in her baby’s head. Blood streamed into the anemic 4-month-old who already has malaria, the mosquito-borne disease that kills a million African children every year.

“Malaria is one of the deadliest sicknesses for children,” the nurse said—words that sent the young mother into a crumpled heap on the bed beside her wide-eyed baby boy, wrapped in a blue-and-yellow floral blanket.

There is new hope, however, in this verdant area where President Barack Obama’s relatives live. A vaccine that appears to be able to prevent the disease in about 50 percent of children, is now undergoing the final stage of testing.

If regulators determine the vaccine is safe, it could be on the market in three to five years—the first vaccine against a human parasite.

Tens of millions of Africans are plagued by malaria every year, and more than a third of the hospital beds in this rural Kenyan region next to Lake Victoria are dedicated to its victims. More than 1 million children die of the disease in Africa annually, a crippling economic drain that prolongs a cycle of disease and poverty throughout the continent.

Malaria is also prevalent in parts of Asia, the Middle East and Central and South America.

This vaccine was developed specifically for Africa, however, and will only prevent the African strain of the disease. Experts say it would be a historic advancement.

“Some may say, ’50 percent, that’s not great.’ And that’s true. If you get a measles vaccine, you’re not going to get measles again,” said Dr. Dave Jones, a U.S. Army colonel and director of a clinic in nearby Kombewa operated by the Walter Reed Army Institute of Research and the Kenya Medical Research Institute.

“But at the same time, when you consider we lose 1 million kids a year, if you could cut that in half it would be a great step forward.”