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The problem
Intervention: Pertussis vaccination following the routine immunization schedule with doses at specified ages
Who it was tested with: 2,842,942 children born in Zhejiang Province, China between 2015 and 2022, followed until age 5 or pertussis diagnosis.
Children or communities are compared with a group that did not receive the intervention, or followed over years. This is the design that best separates what the intervention did from everything else that changed.
"This retrospective cohort study analyzed 2,842,942 children born in Zhejiang between 2015 and 2022, using linked records from the Zhejiang Provincial Immunization Information System and the National Notifiable Disease Surveillance System. Children were followed until pertussis diagnosis, age five, or December 31, 2023. Age-dose-specific and age-vaccination status-specific incidence rates (per 100,000 person-years) were calculated across ten age intervals...Poisson regression assessed the pertussis risk by time since fourth dose." This is a large population-based cohort with systematic data linkage and stratified analysis by age and dose, providing robust evidence of dose-dependent protection with documented waning immunity.
Observational design using administrative records; causality cannot be established and unmeasured confounders may be present; results specific to one Chinese province may not generalize elsewhere
Across countries and designs
3 studies · 2 countries
