Teo Pollastrini / CC BY-SA 4.0
Valneva, the vaccine developer based in Lyon, France, reported positive Phase 2 results for its Shigella vaccine candidate S4V2 on November 9, with antibody responses in Kenyan infants and a reduction in disease in a controlled U.S. adult challenge trial. The company is still reviewing the full data to decide the candidate’s next development steps.
The two studies answer different questions. The infant trial measured safety and immune responses, not whether vaccination prevented infection. The adult trial deliberately exposed volunteers to one Shigella strain under controlled conditions. Neither result establishes how well the candidate would protect children against disease in everyday settings, and S4V2 is not an approved vaccine.
In its full results announcement, Valneva said the infant study enrolled 110 nine-month-olds in Kenya. Researchers compared two dose levels of S4V2 with a meningococcal control vaccine, using a two-dose schedule.
After the second dose, antibody levels against all four targeted Shigella serotypes rose significantly compared with the control group, the company said. Levels peaked after that dose and remained above their starting levels six months later. That is evidence of an immune response and its persistence, rather than a direct measure of protection against illness.
Most reported adverse events in the infant study were mild or moderate, according to Valneva, and did not differ statistically from those in the control group. The company said all treatment-related adverse events resolved without complications. It also said dose selection and vaccination schedules need further evaluation.
The separate U.S. study involved approximately 120 healthy adults aged 18 to 50 across three clinical sites. After an initial dose-selection step, newly enrolled participants received two doses of vaccine or placebo one month apart. About one month after the second vaccination, they were exposed to the Shigella sonnei 53G strain.
Valneva said that trial met its primary endpoint, with a statistically significant reduction in shigellosis caused by the sonnei serotype in vaccinated participants compared with the placebo group. The release did not provide an efficacy percentage, disease-event counts, a confidence interval or a p-value. Further efficacy and immune-response analyses are continuing.
Those missing details matter to judging the size and precision of the effect. The candidate targets four serotypes, but the challenge result described in the announcement concerns one strain of one serotype. It should not be read as proof of equal protection against all four, or as a measure of real-world effectiveness.
LimmaTech sponsored both studies, and Gates Foundation funding supported the infant trial. For Valneva, the results provide evidence to guide decisions about a development programme, but not a finished product or a launch date. The company has not yet set out the next trial stage or its timetable in this announcement.
Shigellosis is a bacterial diarrheal illness. Valneva describes a need for prevention as resistance makes antibiotic treatment harder. The immediate development question is whether the immune responses and controlled challenge result can support a vaccine programme with the evidence needed for broader use. The company says its review of the complete datasets will inform what happens next.
JBizNews Desk | Lyon, France
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