An oral vaccine candidate protected adults against a drug-resistant gut infection in a small early trial

A small, peer-reviewed U.S. trial showed that two oral doses of a Shigella vaccine candidate protected healthy adults from shigellosis in a controlled inpatient challenge. Shigellosis, a bacterial diarrheal infection spread through contaminated food, water, and surfaces, has no approved vaccine.

The disease sickens roughly 450,000 Americans and at least 80 million people worldwide each year, with children under 5 most at risk of severe disease and death. About 242,000 U.S. cases are already resistant to at least one antibiotic.

In a double-blind Phase 2 trial published June 30, 2026 in The Lancet Infectious Diseases00224-0/fulltext), researchers gave 108 adults ages 18 to 49 with low prior exposure to Shigella sonnei either two doses of the live-attenuated WRSs2 vaccine or a placebo, then challenged them in an inpatient setting a month later. A Cincinnati Children's press release reports 89% protection. Coauthor Nadine Rouphael of Emory said the protection was higher than in most prior Shigella vaccine studies. Two participants did not continue after developing severe shigellosis.

Only healthy adults were enrolled, at a single U.S. site, with no real-world transmission data. Shangxin Yang, an uninvolved molecular microbiologist, called the result "highly encouraging" but warned a confirmatory trial would take three to six years. The heaviest burden sits in endemic countries the trial has not yet touched.