Oral Vaccine CVD 1902 Shows Promise Against Salmonella Paratyphi A

In an Oxford University-led study, CVD 1902, an oral live-attenuated vaccine, showed 73% efficacy in a phase 2b controlled human infection mode. Clinical attack rates were 21% in vaccine recipients versus 75% in placebo.

No serious vaccine-related adverse events were reported; reactogenicity was limited to mild–moderate symptoms. Demonstrating protection with an oral live-attenuated formulation in a controlled human infection model is a practical advance given the prior lack of paratyphoid-specific vaccines.

Although serologic assays quantified antibody responses and immunologic assessments explored correlates of protection, standardized functional assays and longitudinal sampling remain necessary for validation.

Attack rates of 21% versus 75% translate to an estimated 73% protection in this controlled exposure setting, but the small sample size and the artificial exposure conditions of a CHIM limit direct extrapolation to heterogeneous field conditions. Nevertheless, the phase 2b CHIM provides strong proof-of-concept that warrants larger, geographically diverse field evaluations to establish real-world effectiveness and inform regulatory decisions.