Immunogenicity and Tolerability of Booster Typhoid Conjugate Vaccine (TCV) 5-6 Years After Initial Dose in Children in Burkina Faso

This study evaluated the persistence of immunity following primary typhoid conjugate vaccination in early childhood and assessed the immunogenicity and safety of a booster dose administered 5-6 years later. Children previously enrolled in a Phase 2 randomized clinical trial of Vi-tetanus toxoid conjugate vaccine (Vi-TT) were re-enrolled at 6-7 years of age. Participants who previously received Vi-TT received a booster dose of Vi-CRM, while control participants received their first TCV dose. Anti-Vi IgG antibody responses were measured at baseline and 28 days post-vaccination. Safety was assessed through solicited and unsolicited adverse events. This study provides data on durability of TCV immunity and the potential role of booster dosing in endemic settings.

Inclusion Criteria: * Male or female children previously enrolled in the 2018-2019 Phase 2 typhoid conjugate vaccine trial * Residence within study area * Parent/guardian provides informed consent Exclusion Criteria: * Receipt of blood products within 6 months * Prior typhoid conjugate vaccine receipt outside the study * Medical condition interfering with evaluation * Acute illness or fever prior to vaccination (temporary exclusion)