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The problem
Intervention: Introduction of typhoid conjugate vaccine (TCV) in 2019 as part of public health response
Who it was tested with: 3,401 typhoid cases in Harare, Zimbabwe stratified by district, age group, and vaccination coverage from 2017-2024.
The same group is measured before the intervention and again afterwards, with a baseline and an endline and sometimes a midline. Change is visible, but other causes cannot be ruled out.
"Data from 3401 typhoid cases during 2017-2024 were analyzed. Attack rates, risk ratios, AMR, and vaccine effectiveness across prevaccine (2017-2019) and postvaccine (2020-2024) periods were compared." The design measures the same population before and after vaccine introduction without a contemporaneous unexposed comparison group, making this a PRE_POST study that demonstrates the vaccine reduced typhoid incidence substantially, particularly in children.
The before-and-after design cannot definitively isolate the vaccine's effect from concurrent infrastructure improvements, behaviour changes, or other public health interventions. Varying effectiveness across subdistricts and the observation of ongoing transmission suggest confounding factors were not fully controlled. The study does not explain the marked variation in vaccine effectiveness between districts.
Across countries and designs
2 studies · 2 countries
