A vaccine against one of the world’s deadliest causes of diarrhoeal disease has cleared an important hurdle, with positive results from two Phase 2 trials announced on Monday.
Valneva said its tetravalent vaccine candidate, known as S4V2, was safe and produced encouraging immune responses in infants, and met its main goal in a controlled human infection study in adults. There is currently no licensed vaccine against shigellosis.
Shigella bacteria cause an estimated 165 million infections a year, including about 62 million in children under five, and up to 600,000 deaths annually, according to the US Centers for Disease Control and Prevention. The disease is the second leading cause of fatal diarrhoeal illness worldwide and a major burden in low- and middle-income countries, where growing antibiotic resistance is making infections harder to treat.
In the infant trial, conducted in Kenya and funded by the Gates Foundation, 110 nine-month-old babies received two doses of S4V2 or a control meningococcal vaccine. The vaccine was well tolerated, with most side effects mild to moderate and no different from the control group, and it produced statistically significant increases in antibodies against all four targeted Shigella serotypes. Antibody levels peaked after the second dose and remained above baseline six months later.
In the second trial, about 120 healthy adults aged 18 to 50 in the United States received two doses of S4V2 or a placebo, then were deliberately exposed to a strain of Shigella sonnei about a month later. The trial met its primary endpoint, with a statistically significant reduction in shigellosis among those who received the vaccine compared with placebo.
Hanneke Schuitemaker, Valneva’s chief scientific officer, said the results were “positive and encouraging” but underlined the need for further clinical evaluation. The company said it was assessing the full datasets to design the next stage of development, including dose selection and vaccination scheduling.
The US Food and Drug Administration granted the vaccine candidate fast-track designation in 2024. LimmaTech sponsored both trials.
Note: these results come from a company announcement and have not yet been published in a peer-reviewed journal; the efficacy findings in adults are preliminary and further analysis is ongoing.
Sources: Valneva press release, “Valneva Announces Positive Phase 2 Results for Tetravalent Shigella Vaccine Candidate S4V2”, 9 November 2026 — https://addonnews.com/valneva-announces-positive-phase-2-results-for-tetravalent-shigella-vaccine-candidate-s4v2/400064/ (GlobeNewswire release).
