Impact of dosing interval on immunogenicity following a heterologous typhoid conjugate vaccine booster in Nepalese children: An observational study

Summary: Objectives: Typhoid conjugate vaccines (TCVs) are essential for controlling endemic typhoid fever in low- and middle-income countries. However, evidence suggests that TCV-induced protection wanes 3–5 years post-vaccination, particularly among children vaccinated before two years of age, raising the question of whether a booster dose is needed. This study leverages a unique context in Nepal, where the nationwide rollout of the Vi-CRM197 TCV occurred four years after a large-scale TCV efficacy trial using Vi-TT, allowing the study to assess the immunogenicity of a heterologous prime-boost schedule.