Maternal immunization with tetanus, diphtheria, and acellular pertussis (Tdap) vaccine during the third trimester of pregnancy, compared with no immunization, was associated with higher neonatal concentrations of pertussis toxin antibodies. This according to a recent prospective, observational, cohort study of term neonates in Houston, TX, from December 2013 to March 2014. The primary outcome was geometric mean concentrations (GMCs) of pertussis toxin antibodies in cord blood of Tdap-exposed and Tdap-unexposed neonates and proportions of Tdap-exposed and Tdap-unexposed neonates with pertussis toxin antibody concentrations of 15 IU/mL or higher, 30 IU/mL or higher, and 40 IU/mL or higher. Researchers found:
- Among 626 pregnancies (mean maternal age 29.7 years, 41% white, 27% Hispanic, 26% black, 5% Asian, 1% other; mean gestation, 39.4 weeks), 312 women received Tdap vaccine at a mean gestation of 31.2 weeks and 314 were unimmunized.
- Neonates whose mothers received Tdap immunization in the third trimester had a geometric mean concentration of pertussis toxin antibodies in cord blood of 47.3 IU/mL vs 12.9 IU/mL, a difference that was statistically significant.
- Concentrations of cord blood antibodies were highest when immunization occurred at 27 to 30 weeks and declined thereafter.
Healy CM, Rench MA, Swaim LS, et al. Association between third-trimester Tdap immunization and neonatal pertussis antibody concentration. JAMA. 2018;320(14):1464–1470. doi:10.1001/jama.2018.14298.
This study underscores the exact reason that we vaccinate pregnant women every pregnancy. Since pertussis causes the most morbidity and mortality in the first 2 months of age, maternal immunity is a key to protecting this vulnerable population. There is not a standalone pertussis vaccine and perhaps with every pregnancy indication our vaccine manufacturers might consider developing one. — John Russell, MD