Healy CM, et al. - Researchers conducted this prospective, observational, cohort study to assess pertussis toxin antibody concentrations in cord blood from neonates born to women immunized and unimmunized with tetanus, diphtheria, and acellular pertussis (Tdap) vaccine in pregnancy and optimal gestational age for immunization to maximize concentrations of neonatal antibodies. Findings suggested an association of immunization with Tdap vaccine during the third trimester of pregnancy with higher neonatal concentrations of pertussis toxin antibodies vs no maternal immunization. An association was found between immunization early in the third trimester and the highest concentrations.

Methods

• Researchers performed this investigation on term neonates in Houston, TX (December 2013-March 2014).
• 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, cutoffs representing quantifiable antibodies or levels that may be protective until the infant immunization series begins, were the primary outcomes.
• The ideal gestation for immunization to achieve maximum pertussis toxin antibodies was the secondary outcome.

Results

• In this analysis, 626 pregnancies (mean maternal age, 29.7 years; 41% white, 27% Hispanic, 26% black, 5% Asian, 1% other; mean gestation, 39.4 weeks) were included.
• It was observed that 312 women received Tdap vaccine at a mean gestation of 31.2 weeks (range, 27.3-36.4); 314 were unimmunized.
• Findings revealed that GMC of neonatal cord pertussis toxin antibodies from the Tdap-exposed group was 47.3 IU/mL (95% CI, 42.1-53.2) vs 12.9 IU/mL (95% CI, 11.7-14.3) in the Tdap-unexposed group, for a GMC ratio of 3.6 (95% CI, 3.1-4.2; P < .001).
• It was noted that more Tdap-exposed than Tdap-unexposed neonates had pertussis toxin antibody concentrations of 15 IU/mL or higher (86% vs 37%; difference, 49% [95% CI, 42%-55%]), 30 IU/mL or higher (72% vs 17%; difference, 55% [95% CI, 49%-61%]), and 40 IU/mL or higher (59% vs 12%; difference, 47% [95% CI, 41%-54%]); P < .001 for each analysis.
• Data reported that GMCs of pertussis toxin antibodies were highest when Tdap vaccine was administered during weeks 27 through 30 and declined afterwards, reaching a peak at week 30 (57.3 IU/mL [95% CI, 44.0-74.6]).