Persistent Efficacy of Vi Conjugate Vaccine against Typhoid Fever in Young Children

To the Editor: The limitations of the three licensed typhoid vaccines that precluded their use in children younger than five years old have been overcome by a Vi conjugate vaccine (Vi-rEPA, a conjugate of the capsular polysaccharide of Salmonella typhi, Vi, bound to nontoxic recombinant Pseudomonas aeruginosa exotoxin A [rEPA]).1–3 After 27 months of active surveillance in a double-blind, placebo-controlled, randomized trial involving 12,008 children two to five years old in the Mekong Delta region of Vietnam, Vi-rEPA was found to confer 91.1 percent protection against typhoid.3,4 Vi-rEPA induced an increase by a factor of 10 or more . . .