A landmark Shigella vaccine trial conducted with key contributions from Cincinnati Children’s Hospital Medical Center has delivered a breakthrough result — 89% protection against Shigella sonnei infection. Published in The Lancet Infectious Diseases, the findings mark the most significant step forward in over a century of efforts to develop a licensed vaccine against one of the world’s most persistent and dangerous diarrheal diseases.
What Is Shigella and Why Does It Matter?
Shigella is a highly contagious bacterium responsible for severe diarrheal illness across the globe. It spreads through contaminated food and water, as well as direct person-to-person contact — making it especially dangerous in crowded settings such as childcare centers, military deployments, and communities with limited access to clean water.
The Scale of the Global Shigella Burden
Every year, tens of millions of people worldwide contract a Shigella infection, and hundreds of thousands die as a result. Children between the ages of one and five are disproportionately affected, often suffering the most severe outcomes including hospitalization and death. In the United States alone, roughly 450,000 Shigella infections are recorded annually, resulting in more than 5,000 hospitalizations and dozens of fatalities.
The Growing Threat of Antibiotic Resistance
What makes Shigella especially alarming from a public health standpoint is its increasing resistance to antibiotics. As first-line treatments become less effective, the global medical community faces mounting urgency to develop preventive solutions. Despite more than 100 years of sustained research, no licensed Shigella vaccine has ever reached the market — until now, progress was stalled. That is why the new Shigella vaccine trial results carry such enormous significance.
The WRSs2 Vaccine Candidate: How It Works
The vaccine evaluated in this new study is called WRSs2, an oral, live-attenuated vaccine candidate specifically designed to target Shigella sonnei — the strain more commonly associated with outbreaks in higher-income countries. Unlike injectable vaccines, WRSs2 is taken by mouth and uses a live but deliberately weakened form of the bacterium to stimulate immune protection without triggering full-blown disease.
Trial Design and Participant Details
The Phase 2 clinical trial enrolled 108 healthy adult volunteers between the ages of 18 and 49, with enrollment running from October 11, 2022, through January 9, 2024. Of those enrolled, 73 participants completed the controlled human infection model — also known as a challenge phase — in which vaccinated and placebo groups were deliberately exposed to Shigella sonnei to directly measure the vaccine’s protective effects.
Key Efficacy and Safety Findings
Two doses of the WRSs2 vaccine demonstrated 89% protection against Shigella sonnei infection compared to placebo — a result that substantially surpassed efficacy rates reported in previous Shigella vaccine trials. Beyond preventing illness altogether, vaccinated participants also experienced less severe symptoms and shed fewer bacteria, suggesting the vaccine may reduce disease transmission within communities. A small number of participants did report temporary side effects, prompting dosing adjustments during the trial. Crucially, no serious adverse vaccine-related events were reported, supporting a favorable safety profile.
Cincinnati Children’s Leading Role in the Research
Cincinnati Children’s Hospital Medical Center played a central role in advancing this Shigella vaccine trial. Robert Frenck, MD — a pediatrician, professor in the Division of Infectious Diseases, and director of the hospital’s Vaccine Research Center — served as a joint senior author of the study, contributing to trial design, clinical oversight, and funding acquisition.
The Research Team Behind the Results
Additional contributors from Cincinnati Children’s included Michelle Dickey, NP (clinical investigation), Christina Quigley, PhD (methodology and data validation), Tena Pham, RN (clinical conduct), Josh Adams, BS (data collection), and Gaurav Kwatra, PhD (research and analysis). Together, the team brought a multidisciplinary approach that strengthened both the rigor and credibility of the trial.
Dr. Frenck underscored the importance of the milestone: “This study represents an important step forward in developing a safe and effective vaccine against Shigella. With continued research, we have the potential to significantly reduce the global burden of this disease, particularly among children.”
What Comes Next for the Shigella Vaccine?
The results of this Phase 2 trial support advancing WRSs2 into larger-scale clinical studies. Future research will prioritize testing in high-risk populations — particularly children living in regions where Shigella is endemic — as well as evaluating long-term protection, refining dosing strategies, and expanding coverage to protect against multiple Shigella strains beyond sonnei.
Collaborative Development and Funding
The WRSs2 vaccine is not yet commercially manufactured. Its development is advancing through collaboration among government agencies, military researchers, and academic institutions. Funding for the current study was provided by the National Institutes of Health, with pharmaceutical support from the U.S. Department of Defense. Contributing institutions included Emory University’s Hope Clinic of the Emory Vaccine Center, the National Institute of Allergy and Infectious Diseases, the Emmes Company, Walter Reed Army Institute of Research, and the Naval Medical Research Command.
Implications for Global Pediatric Health
Should larger trials confirm and extend the Phase 2 findings, WRSs2 could become the first-ever licensed vaccine against Shigella — a milestone with profound implications for child health in low- and middle-income countries, travelers, military personnel, and vulnerable communities worldwide. The success of this Shigella vaccine trial opens a realistic path toward eliminating one of the most preventable causes of childhood mortality globally.
