Comparative study on safety and immunogenicity of homologous versus heterologous prime-boost Typhoid Conjugate Vaccine (TCV) schedules in Nepalese children
Typhoid fever; evaluation of booster typhoid conjugate vaccination schedules and immunogenicity in children previously vaccinated with typhoid conjugate vaccine.
This study is a randomised, observer- and participant-blind, parallel-group comparative study in children in Kathmandu Valley, Nepal, who were previously vaccinated with Vi-CRM197 typhoid conjugate vaccine. Participants will be randomised 1:1 by computer to receive either a homologous booster (Vi-CRM197) or a heterologous booster (Vi-TT/Typbar-TCV). Follow-up will continue for approximately 18 months and will include immunogenicity blood sampling, safety monitoring, scheduled follow-up visits and passive surveillance for enteric fever outcomes.
Children living in Kathmandu Valley, Nepal, who: 1. Previously received a single dose of Vi-CRM197 typhoid conjugate vaccine at 15–20 months of age through the national immunisation programme or catch-up campaign 2. Are at least 4 years post-primary vaccination at enrolment (typically aged 5–6.5 years) 3. Have verifiable documentation of prior vaccination 4. Are in good health on the day of vaccination according to the attending doctor 5. Have a parent/legal guardian willing and able to provide informed consent and support study follow-up 6. Live within the study catchment area
1. Unable to provide verifiable documentation of prior Vi-CRM197 vaccination 2. Known allergy to any vaccine component 3. Any medical or social condition that may prevent compliance with study procedures or follow-up 4. Known congenital or acquired immunodeficiency that could affect vaccine responses 5. Planning to move away from the study catchment area during follow-up 6. Temporary exclusion at the time of vaccination due to reported fever within the previous 24 hours or receipt of another vaccination within the previous 48 hours