From Crisis to Control: A Study of Typhoid Conjugate Vaccine Efficacy in Harare, Zimbabwe (2017–2024)

Abstract Background Typhoid fever remains a public health concern in Harare City, Zimbabwe. Recurrent outbreaks are driven by inadequate water, sanitation, and hygiene (WASH) infrastructure. In 2019, Typhoid Conjugate Vaccine (TCV) was introduced. TCV impact on typhoid epidemiology, antimicrobial resistance (AMR), Salmonella Typhi population, and effectiveness across districts and age groups remains understudied. Methods Data from 3,401 typhoid cases during 2017-2024 were analyzed. Attack rates, risk ratios, AMR, and vaccine effectiveness across pre-vaccine (2017–2019) and post-vaccine (2020–2024) periods were compared. Analysis was stratified by district, vaccination coverage, and age groups. Genomic characteristics of Salmonella Typhi strains isolated post-vaccination were investigated and compared to pre-vaccine population. Results Attack rates for Western district, which reported 70·8% of cases, decreased from 1373/100,000 before TCV to 341/100,000 after (risk ratio:0·40,P=0·0001). Sub-districts had attack rates of 1,783(Glen View), 1,687(Mufakose), and 1,145(Budiriro) per 100,000 before vaccination and 223, 33, and 364/100000 respectively, after (risk ratio: 0·22, 0·03, 0·48, respectively, P 0·0001). The 0–15 age group showed vaccine effectiveness of 81·2% (95% CI 71·2- 88·8), as compared to 61·4% (95% CI 54·3- 68·1) across all ages. Genomic comparison of Salmonella Typhi isolates pre-and post-vaccination did not indicate changes in bacterial population. AMR phenotypic data and genomic prediction indicated lower resistance to antibiotics post-vaccination. Conclusion TCV reduced typhoid incidence, particularly in high-burden areas and children. No shift in Salmonella Typhi population was observed. Ongoing transmission underscores need for integrated measures, including human-resource capacity, improved WASH infrastructure, research on vaccine performance variability and refined multi-sectoral interventions.