The results, published in The Lancet Infectious Diseases this summer: It was 89% effective at preventing one of the leading causes of diarrheal deaths, shigellosis. No Shigella vaccine has ever been licensed, despite more than 100 years of research. While one of the most common causes of diarrheal deaths, it's part of a group of triggering bacteria. Frenck imagines a combination vaccine that would protect against all the major bacterial causes of diarrheal deaths, albeit likely not cyclosporiasis. "The most important population for a potential Shigella vaccine would be children under 5," Talaat says.