Effect of dosage on immunogenicity of a Vi conjugate vaccine injected twice into 2- to 5-year-old Vietnamese children.

In a double-blind, randomized, and placebo-controlled previous trial, the efficacy of Vi-rEPA for typhoid fever in 2- to 5-year-olds was 89.0% for 46 months. Vi-rEPA contained 25 microg of Vi and induced a greater-than-eightfold rise in immunoglobulin G (IgG) anti-Vi in all of the vaccinees tested.