Efficacy of WRSs2, a live-attenuated Shigella sonnei vaccine, against shigellosis in a controlled human infection model in the USA: a phase 2, double-blind, randomised, placebo-controlled trial.
Nadine Rouphael, Shahida Baqar, Michelle Dickey et al.
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In 30 seconds
This phase 2, double-blind, randomised, placebo-controlled trial assessed the safety and efficacy of live-attenuated Shigella sonnei vaccine WRSs2 in healthy US adults aged 18–49 years using a controlled human infection model. After oral challenge, adjudicated shigellosis occurred in 3 (9%) of 34 participants given pooled two-dose vaccine and 21 (81%) of 26 placebo recipients. Estimated vaccine efficacy was 89% (95% CI 71–96; p<0·0001). Six participants experienced grade 3 post-vaccination adverse events; no vaccine-related serious adverse events or deaths occurred.
Key findings
- Shigellosis occurred in 3 (9%) of 34 pooled two-dose vaccine recipients versus 21 (81%) of 26 placebo recipients.
- Vaccine efficacy against adjudicated shigellosis was 89% (95% CI 71–96; p<0·0001).
- Six participants had grade 3 post-vaccination adverse events; no vaccine-related serious adverse events or deaths occurred.
Why it matters
Shigella remains an important cause of bacterial diarrhoea and dysentery, and no licensed vaccine is available. The substantial protection observed in this controlled challenge study supports continued evaluation of WRSs2 and related live-attenuated candidates, while the adverse events underscore the need to refine the balance between protection and tolerability.
What to keep in mind
The study involved healthy adults in the USA and used an experimental challenge model; its findings may not establish effectiveness in routine exposure settings or other populations.