UCLA

Background. Pertussis is a highly contagious respiratory disease, for which maternal tetanus-diphtheria-acellular pertussis (Tdap) vaccination during pregnancy is the primary prevention strategy in infants. In October 2011, the CDC Advisory Committee on Immunization Practices (ACIP) recommended Tdap vaccination for all unvaccinated pregnant women. In 2012, ACIP extended this recommendation to include all pregnant women, regardless of previous vaccination. The effects of these recommendations in the United States (US) on infant pertussis morbidity and mortality are currently unknown. Objectives. To examine the impact of the 2011/2012 ACIP pertussis recommendation on pertussis morbidity and mortality among US infants. Methods. We used monthly data of pertussis deaths among infants <1 year from January 2005 to December 2017 in the CDC Linked Birth/Infant Death Data to perform an interrupted time series (ITS) analysis. We compared trends in pertussis mortality at <1 year before and after the guideline changes. We fit segmented quasi-Poisson regression models for pertussis deaths with monthly live births as an offset to estimate the time trend during three time periods: pre-recommendation, transition, and post-transition. To account for possible bias due to trends in access to healthcare following the 2010 Affordable Care Act (ACA), four comparative and controlled ITS analyses were conducted. These included maternal age stratified analyses, number of prenatal care visit stratification, adequacy of prenatal care utilization (APNCU) stratification, and a behavior-based control. Results. 156 months of data were included in the analysis. No appreciable differences in trend were found in infant pertussis morbidity or mortality after the guideline changes in both the adjusted and unadjusted models. These results were similar for in sensitivity analyses that varied the timing of the transition and post periods and varied the existence of the transition period. Conclusions. The 2011/2012 ACIP maternal pertussis vaccination recommendations were not associated with a change in trend in infant pertussis morbidity or mortality in the US between 2005 and 2017. Future analyses should include geographic data from the CDC in order to more directly account for the ACA Medicaid Expansion. Future analyses should also investigate heterogeneity in recommendation implementation and whether those infants at highest risk of pertussis mortality are being reached by this preventative strategy.