Vaccine Development Against Salmonella Typhi: The Search is Still On

Abstract

Salmonella serovar typhi infection still remains a serious problem in South Asia, South-East Asia, and sub-Saharan Africa. The emergence of multidrug resistance, lack of proper diagnosis and chronic typhoid carrier are the main causes of such a high level of morbidity and mortality. Presently, three vaccines have been licensed for typhoid infection but none of them is optimum for complete eradication for want of safety and long lasting immunity. Several subunit and attenuated candidate vaccines are under trial. Recently, in India Typbar TCV conjugate vaccine has been licensed. However, this vaccine being subunit may not induce appropriate immune response and also it cannot be given to infants. We need a multivalent attenuated vaccine which can induce both cellular as well as humoral immunity against different pathogenic serovar of Salmonella. Live attenuated vaccine could be an attractive choice taking care of all the above points. In this review, we focus on the pathogenesis of Salmonella serovar typhi, role of humoral as well as Cell-Mediated Immune (CMI) response, different licensed vaccines with their pros and cons, and also the targets which are already been put on clinical trials. We have discussed the attenuation of the candidates by modification of certain structural and functional genes especially looking for induction of CMI.

Keywords

• candidate vaccine
• cell-mediated immune response
• live attenuated