A NEW Salmonella Paratyphi A vaccine may fill a critical gap in preventing enteric fever, which affects more than two million people worldwide annually. The VASP Study Team conducted a double-blind, randomised, placebo-controlled trial in healthy UK adults to test the efficacy, safety, and immune response of the orally administered live attenuated vaccine CVD 1902.
Strong Efficacy Against S. Paratyphi A Infection
In the trial, 72 participants received either two doses of CVD 1902 or placebo, spaced 14 days apart, followed by an oral challenge with S. Paratyphi A 28 days after the second dose. In the intention-to-treat population, only 21% of vaccinated participants developed infection compared to 75% in the placebo group, yielding a vaccine efficacy of 73% (95% CI, 46–86%). The per-protocol analysis confirmed these results with 69% efficacy (95% CI, 42–84%).
The vaccine also induced strong immune responses, with significant serum IgG and IgA antibody production targeting the O antigen of S. Paratyphi A. No immune response was detected in participants receiving placebo.
Safety Profile of the Salmonella Paratyphi A Vaccine
Safety was closely monitored during the trial. The number and type of adverse events were similar between the vaccine and placebo groups, and no serious vaccine-related events were reported. This confirms that CVD 1902 is well-tolerated, supporting its potential use in larger populations.
Implications for Public Health
The successful development of a Salmonella Paratyphi A vaccine addresses a major unmet need in global health. If confirmed in larger trials, this oral, two-dose vaccine could provide a practical, effective tool to prevent enteric fever, particularly in endemic regions. The strong immune response and favorable safety profile suggest that CVD 1902 could be widely implemented, offering protection for millions of at-risk individuals.
Reference
McCann N et al; VASP Study Team. Safety, efficacy, and immunogenicity of a salmonella paratyphi a vaccine. N Engl J Med. 2025;393(17):1704-14.
