Researchers say a phase 2 trial found promise for a Shigella vaccine candidate.
Why it matters: Shigella is a major cause of severe diarrheal disease, especially for young children in low-income countries. A vaccine that works in the real world could fill a major global-health gap where no licensed Shigella vaccine is in routine use.
- The vaccine candidate, WRSs2, is a live-attenuated Shigella sonnei vaccine.
- The phase 2 randomized, placebo-controlled human infection study enrolled healthy adults at two U.S. sites.
- Participants were enrolled between Oct. 11, 2022, and Jan. 9, 2024, and were later challenged with virulent S. sonnei 53G.
- WHO estimates Shigella causes 28,000 to 64,000 under-5 deaths annually in low- and middle-income countries.
A phase 2 study of a live-attenuated Shigella sonnei vaccine candidate, WRSs2, showed efficacy in a controlled human infection model in the U.S., according to the published trial report in PubMed.
The trial was double-blind, placebo-controlled and ran at two U.S. sites. It enrolled healthy adults between Oct. 11, 2022, and Jan. 9, 2024, then used a challenge model with virulent S. sonnei 53G after vaccination. ClinicalTrials.gov lists the study as NCT04242264 and says it evaluated safety, reactogenicity, immunogenicity and efficacy of WRSs2.
The public-health case for a vaccine is substantial. WHO says Shigella has a major burden in low- and middle-income countries and estimates it causes 28,000 to 64,000 deaths among children under 5 there each year. WHO also says diarrhoeal disease remains a major killer of young children globally, causing about 443,832 under-5 deaths annually, with bacterial pathogens including Shigella as important causes.
CDC says Shigella infection can cause watery, bloody or prolonged diarrhea, abdominal pain, fever and malaise, and notes there are no licensed Shigella vaccines in routine use. A recent review in the Journal of Infectious Diseases says vaccine development has reached a promising point after decades of effort, but still has not produced a globally licensed vaccine.
The study is an important step, but it is still early. The challenge model involved healthy U.S. adults, so the key unanswered questions are how the vaccine performs in children, in endemic settings and over time.
By the numbers
- 28,000 to 64,000 - WHO estimate of annual under-5 Shigella deaths in low- and middle-income countries
- 443,832 - WHO estimate of annual under-5 deaths from diarrhoeal disease globally
- 108 - participants enrolled in the phase 2 WRSs2 study
Yes, but: The result comes from a controlled human infection study in healthy adults, not a field trial in children or endemic settings.
What's next: Larger field trials and data in children will be needed to show real-world protection and durability.