Valneva reports positive Phase 2 results for its Shigella vaccine candidate S4V2
What's the deal? Valneva, the French-Austrian vaccine company, announced positive results on 9 November 2026 from two Phase 2 trials of S4V2, its candidate vaccine against shigellosis. S4V2 is described as the world's most clinically advanced tetravalent bioconjugate vaccine against this disease — "tetravalent" meaning it targets four variants of the bacterium.
What the data showed: In an infant study in Kenya, 110 infants aged 9 months received two doses of S4V2, which showed a favourable safety profile and encouraging immune responses compared with a control vaccine. In a separate US study using a controlled human infection model — where healthy volunteers are deliberately exposed to the bacterium under supervision to test whether a vaccine works — around 120 adults aged 18 to 50 received S4V2 or placebo. The trial met its primary endpoint: a statistically significant reduction in shigellosis caused by Shigella sonnei among vaccinated participants.
Why it matters: Shigellosis is a severe diarrhoeal disease caused by Shigella bacteria and is the second leading cause of deadly diarrhoeal illness worldwide, with up to 165 million infections each year — over 62 million of them in children under five. There is currently no broadly available vaccine, so a first-in-class candidate that works in infants, the group most affected, would address a major unmet need in low- and middle-income countries. Valneva is now reviewing the full dataset to decide the next stage of development.
Read more: Valneva, 09 November 2026
