Evaluation of immune responses to an oral typhoid vaccine, Ty21a, in children from 2 to 5 years of age in Bangladesh

Abstract Young children are very susceptible to typhoid fever, emphasizing the need for vaccination in under five age groups. The parenteral Vi polysaccharide vaccine is not immunogenic in children under 2 years and the oral Ty21a vaccine (Vivotif) available in capsular formulation is only recommended for those over 5 years. We studied immune responses to a liquid formulation of Ty21a in children 2–5 years of age. Since children in developing countries are in general hypo responsive to oral vaccines, the study was designed to determine if anti-helminthic treatment prior to vaccination, improves responses. In a pilot study in 20 children aged 4–5 years, the immune responses in plasma and in antibody in lymphocyte secretions (ALS) to the enteric coated capsule formulation of Ty21a was found to be comparable to a liquid formulation ( P  > 0.05). Based on this, children ( n  = 252) aged ≥2– The vaccine was well tolerated with only a few mild adverse events recorded in We recommend that safety and efficacy studies with a liquid formulation of the vaccine are carried out in children under five, including those less than two years of age to determine if Ty21a is protective in these age groups and applicable as a public health tool for controlling typhoid fever in high prevalence areas of typhoid fever including Bangladesh.