In the slum of Damagaza in Abuja, Nigeria, twin toddlers Hassana and Husseina drank water from the only source near their home: a stream. Shortly after, little holes appeared in their intestines, a complication from typhoid fever, and the babies died.

The stream water they drank was contaminated with bacteria from the urine or feces of typhoid-infected people.

Every year, typhoid fever infects about 22 million people and kills more than 200,000. The illness is especially dangerous for children in Latin America, sub-Saharan Africa and South Asia, but scientists now say they have developed a vaccine that can prevent the illness in children as young as six months, the BBC reports.

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It’s the first typhoid vaccination that is safe for infants and is a crucial public health win, especially for communities — like Hassana and Husseina’s — that lack clean water and safe sanitation systems.

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Researchers say the vaccine is vital because typhoid bacteria has developed resistance to antibiotics, rendering the medicine ineffective. The illness causes high fevers, headaches, nausea, constipation and, sometimes, skin rashes. Meanwhile, typhoid fever survivors can suffer from perforated intestines and heart problems.

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Already, the World Health Organization (WHO) has promoted the use of the new vaccine in children six-months and older in low- and middle-income countries where typhoid fever persists.

"It could have a huge impact,” Oxford University Professor Andrew Pollard told the BBC. Pollard conducted clinical trials in England and the results were published in a medical journal last month. The vaccine was found to be 87% effective — meaning it could save thousands of lives

As part of  the trial, more than 100 people took the new vaccine and then purposely infected themselves with the typhoid-causing bacteria to see if the vaccine worked. Tests like these enable scientists to quickly study the effectiveness of new vaccines rather than spending years studying the vaccine in at-risk communities.

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In the United States, about 5,700 people develop typhoid fever each year, usually after traveling internationally, the Centers for Disease Control and Prevention reports.

Handwashing with soap, especially after using the bathroom and before preparing food, helps prevent the disease from spreading. So programs that raise awareness of good hygiene practices — like water and sanitation programs — along with this new vaccine, could help reduce future incidences of typhoid.