The need & the issues related to new-generation typhoid conjugate vaccines in India

Abstract

The low- and middle-income countries bear the highest burden of typhoid fever in the world. India, along with other South Asian countries, has a significant incidence of typhoid fever among young children though there is a paucity of published data on community burden. In spite of the availability of Vi-polysaccharide (Vi-PS) and conjugated Vi-PS vaccines, these are not adequately utilized in India and in the neighbouring countries. To address many shortcomings of the unconjugated Vi-PS vaccines, typhoid conjugate vaccines (TCVs) are developed by conjugating Vi-PS with different carrier proteins. Three such vaccines using tetanus toxoid as a carrier protein are already licensed in India. Several other Vi-PS conjugates are currently in various stages of development. The current review provides an update on the existing and upcoming new TCVs along with a detailed discussion on the various issues involved with their clinical use and limitations.

Keywords: Conjugate Vi-polysaccharide vaccines; Vi-polysaccharide vaccines; typhoid; typhoid vaccines.

Fig. 1

Typhoid conjugate vaccine pipeline: Different licensed and candidate typhoid conjugate vaccines in various phases of development and licensure. ^*Under review for national licensure. WHO PQ, WHO pre-qualification; LIBP, Lanzhou Institute of Biological Products Co. Ltd., PR China; Vi-TT, Vi conjugated with tetanus toxoid; Vi-rEPA, Vi recombinant exoprotein antigen; Vi-CRM, Vi conjugated with cross reacting material; Vi-DT, Vi conjugated with diphtheria toxoid. Source: Adapted from Ref. .

Fig. 2

Levels of anti-Vi IgG of 2-5 yr old children in Vi-rEPA efficacy study stratified according to age. Source: Adapted from Ref. .