Immune responses in children after vaccination with a typhoid Vi-tetanus toxoid conjugate vaccine in Bangladesh
Farhana Khanam, Golap Babu, Nazia Rahman, Xinxue Liu, Nazmul Hasan Rajib, Shams Uddin Ahmed, Md Ismail Hossen, Prasanta Kumar Biswas, Sarah Kelly, Katherine Thesis-Nyland, Yama F Mujadidi, Nigel A.J. McMillan, Andrew J. Pollard, John D. Clemens, Firdausi Qadri
Abstract
A cluster-randomized trial of Vi-TT was conducted in Dhaka, Bangladesh, using JE vaccine as the control. A subset of 1,500 children were randomly selected on 2:1 basis (Vi-TT vs JE) to assess immune response. Blood was collected before vaccination, and on days 28, 545 and 730 post-vaccination and plasma anti-Vi-IgG response was measured. A robust, persistent antibody response was induced after single dose of Vi-TT, even after 2 years of vaccination. While there is no accepted serological antibody threshold of protection, analyzing the antibodies of children who received Vi-TT provides evidence that may later be useful in predicting population protection.