Addressing the silent pandemic - capturing the public health impact of typhoid conjugate vaccine introduction on antimicrobial use

Summary 

Salmonella enterica serovar Typhi (S. Typhi) is the causative agent of typhoid fever and is responsible for over 100,000 deaths annually, particularly among young children in South Asia and sub-Saharan Africa. Typhoid conjugate vaccines (TCVs) were recommended for use in typhoid-endemic areas, particularly those where AMR is a problem, by the World Health Organization (WHO) in 2018. TCVs have been shown to be safe and efficacious across multiple settings, but the evidence base for the impact of TCVs against AMR is scarce. Vaccines may have an impact on antimicrobial resistance (AMR) both through the prevention of infections caused by drug-resistant pathogens (direct effect) and through the reduction of antimicrobial use (AMU, indirect effect) through the prevention of primary and or secondary infections. TCVs have been shown to be effective against extensively drug resistant (XDR, resistant to first-line antimicrobials chloramphenicol, ampicillin, and cotrimoxazole as well as fluoroquinolones and third-generation cephalosporins) S. Typhi in Hyderabad, Pakistan, but the evidence base for the impact of TCVs is still weak. We aim to leverage an ongoing post- TCV introduction impact study in Karachi, Pakistan, where XDR typhoid is prevalent, to assess the impact of TCVs on preventing antimicrobial use among vaccine recipients. By reducing antimicrobial use, TCVs can slow the emergence and spread of AMR among S. Typhi and potentially lead to lower selection pressure on other organisms.