Prenatal tetanus-diphtheria-acellular pertussis vaccine effectiveness at preventing infant pertussis.

• ACIP recommends that pregnant women receive Tdap, ideally at 27–36 weeks' gestation. • Tdap5 vaccination during 27–36 weeks' gestation protects infants from pertussis. • Tdap vaccination of mothers after pregnancy did not protect infants from pertussis. To evaluate the effectiveness of the tetanus, diphtheria, and acellular pertussis (Tdap) vaccine containing five pertussis components (Tdap5; Adacel®, Sanofi) when given during pregnancy at preventing pertussis in infants less than 2 months of age. The US Centers for Disease Control and Prevention (CDC), in collaboration with the Emerging Infections Program (EIP) Network, undertook a case-control study evaluating the effectiveness of Tdap vaccination in pregnancy against pertussis in infants less than 2 months of age based on data collected by the EIP Network from 2011 through 2014. The dataset from the CDC/EIP Network study was used to conduct this product-specific vaccine effectiveness analysis of Tdap5 vaccination in pregnancy to prevent disease in young infants. The main outcome of interest was vaccine effectiveness in infants whose pregnant parents were vaccinated with Tdap5 between 27 and 36 weeks' gestation, in accordance with the ideal timing for Tdap vaccination in pregnancy recommended by the US Advisory Committee on Immunization Practices. Odd ratios (ORs) and 95 % confidence intervals (CIs) were estimated using conditional logistic regression, and vaccine effectiveness was calculated as (1–OR) × 100 %. There were 160 infant pertussis cases and 302 matched controls included in this Tdap5-specific study. Tdap5 effectiveness in preventing pertussis in infants whose pregnant parents were vaccinated between 27 and 36 weeks' gestation was 92.5 % (95 % CI, 38.5 %–99.1 %). Effectiveness of Tdap5 against pertussis-related hospitalization in infants whose pregnant parents were vaccinated between 27 and 36 weeks' gestation could not be calculated due to lack of discordance among matched cases and controls. Vaccination of the parents after pregnancy or less than 14 days before delivery did not protect infants from pertussis. Tdap5 vaccination in pregnancy between 27 and 36 weeks' gestation is highly effective at protecting young infants from pertussis. Study registration: ClinicalTrials.gov , NCT05040802. [ABSTRACT FROM AUTHOR]