N Engl J Med

First modern paratyphoid vaccine shows strong protection against infection

November 5, 2025

Study details: This randomized, placebo-controlled trial evaluated the oral live-attenuated S. Paratyphi A vaccine (CVD 1902) in 72 healthy adults using a controlled human infection model. Participants received two doses and were challenged with S. Paratyphi A, with endpoints including infection rates, immunogenicity, and safety.

Results: Among those challenged, 21% of vaccinated participants developed infection compared with 75% in the placebo group, yielding a vaccine efficacy of 73% (95% confidence interval, 46–86). The vaccine induced robust serum IgG and IgA responses to the O antigen, with no serious vaccine-related adverse events reported. Side effects were mild to moderate and comparable between groups.

Clinical impact: CVD 1902 is the first vaccine to show protection against S. Paratyphi A. If efficacy is confirmed in endemic settings, this oral vaccine could become a critical tool in global enteric fever prevention.

Source:

McCann N, et al; VASP Study Team. (2025, October 30). N Engl J Med. Safety, Efficacy, and Immunogenicity of a Salmonella Paratyphi A Vaccine. https://pubmed.ncbi.nlm.nih.gov/41160821/