OBJECTIVES:
Following the introduction of jurisdictional maternal pertussis vaccination programs in Australia, we estimated maternal vaccine effectiveness (VE) and whether maternal pertussis vaccination modified the effectiveness of the first 3 primary doses of pertussis-containing vaccines.
METHODS:
We conducted a population-based cohort study of 279 418 mother–infant pairs using probabilistic linkage of administrative health records in 3 Australian jurisdictions. Infants were maternally vaccinated if their mother had a documented pertussis vaccination ≥14 days before birth. Jurisdictional immunization records were used to identify receipt of the first 3 infant doses of pertussis-containing vaccines. Infant pertussis infections were identified using notifiable disease records. VE was estimated using Cox proportional hazard models.
RESULTS:
Pertussis was administered during 51.7% (n = 144 429/279 418) of pregnancies, predominantly at 28–31 weeks’ gestation. VE of maternal pertussis vaccination declined from 70.4% (95% confidence interval [CI], 50.5–82.3) among infants <2 months old to 43.3% (95% CI, 6.8–65.6) among infants 7–8 months old and was not significant after 8 months of age. Although we observed slightly lower VE point estimates for the third dose of infant pertussis vaccine among maternally vaccinated compared with unvaccinated infants (76.5% vs 92.9%, P = .002), we did not observe higher rates of pertussis infection (hazard ratio, 0.70; 95% CI, 0.61–3.39).
CONCLUSIONS:
Pertussis vaccination near 28 weeks’ gestation was associated with lower risk of infection among infants through 8 months of age. Although there was some evidence of lower effectiveness of infant vaccination among maternally vaccinated infants, this did not appear to translate to greater risk of disease.