Global patterns of pertussis incidence and vaccination strategies: implications of divergent surveillance data.

Pertussis remains a global threat for infants, and recent increases in notifications have renewed interest in optimising vaccination strategies and improving vaccines. At the biological level, the rationale for maternal pertussis immunization extends beyond passive antibody transfer alone and may also involve broader maternal-infant immune interactions; however, at the population level these mechanisms are operationalized through policy adoption, timing recommendations, and coverage. We compared incidence constructs from WHO routine notifications and Global Burden of Disease (GBD) modelled estimates and assessed how associations with vaccination policy indicators change across outcome definitions. Trends were characterised with Joinpoint regression; policy associations were estimated using Bayesian hierarchical models fitted separately to each dataset with Universal Health Coverage stratified random intercepts. Incidence levels and trends differed markedly between WHO and GBD. Unadjusted analyses showed heterogeneous, sometimes opposing, associations for maternal immunization and schedule timing. After adjustment, most schedule parameters were small and imprecise, whereas DTP3 coverage remained strongly inversely associated with incidence in GBD but not in WHO. Surveillance and modelled estimates should not be interpreted interchangeably; harmonized constructs and routine implementation and ascertainment metadata are needed for robust cross-country inference.