The study is a part of the Typhoid Vaccine Acceleration Consortium (TyVAC), which aims to reduce the global burden of typhoid fever by accelerating the introduction of TCV in low-resource settings. As a part of the TyVAC consortium, independent impact studies are also being conducted in Dhaka, Bangladesh and Blantyre, Malawi.

This study started in November 2017 and has enrolled 20,019 children from nine months to <16 years of age from a predefined catchment area in Lalitpur, Kathmandu (17 wards of Lalitpur).

The children were randomised to receive either Vi-TCV or a control vaccine (Group A meningococcal vaccine). At the same time, a subset of 1500 consenting participants (1000 Vi-TCV, 500 control vaccine) was sub-randomised to have blood samples collected to study immunogenicity.

Participants were followed up in fever clinics set up at all 17 wards of the Lalitpur area and Patan hospital, the main study hospital, to capture confirmed typhoid fever cases. All participants presenting with a fever after two or more days and/or a temperature higher than 38 degrees Celcius consented to blood culture and had their blood samples taken for confirmation of the diagnosis of typhoid fever. The parents or guardians of participants were contacted every three months either via telephone call or an in-person visit to collect information about mortality and morbidity endpoints, including fever, antibiotic use, school/work absenteeism etc.

At the end of the study, all participants were unblinded and offered the alternate vaccine. After the campaign, a census and Global Water, Sanitation, & Hygiene (WASH) survey were also conducted in the catchment area. The final results of this study show that the typhoid conjugate vaccine (Vi-TCV) is efficacious, safe and immunogenic.