Maternal immunization earlier in pregnancy maximizes antibody transfer and expected infant seropositivity against pertussis.

Maternal immunization against pertussis is currently recommended after 26 gestational weeks (GW). Data on the optimal timing of maternal immunization are inconsistent.
 We conducted a prospective observational non-inferiority study comparing the influence of second (GW 13-25) versus third (≥ GW 26) trimester tetanus-diphtheria-acellular pertussis (Tdap) immunization in pregnant women who delivered at term. Geometric mean concentrations (GMC) of cord blood antibodies to recombinant pertussis toxin (PT) and filamentous hemagglutinin (FHA) were assessed by enzyme-linked immunosorbent assay. The primary endpoint were GCMs and expected infant seropositivity rates, defined by birth anti-PT >30 EU/ml to confer seropositivity until 3 months of age.
 We included 335 women (mean age 31.0±5.1 years, mean gestational age 39.3 GW±1.3) previously immunized with Tdap in the second (n=122) or third (n=213) trimester. Anti-PT and FHA GMCs were higher following second versus third trimester immunization (PT: 57.1 EU/ml [95% CI 47.8-68.2] versus 31.1 EU/ml [95% CI 25.7-37.7], p<0.001; FHA: 284.4 EU/ml [95% CI 241.3-335.2] versus 140.2 EU/ml [95% CI 115.3-170.3], p<0.001). The adjusted GMC ratios after second versus third trimester immunization were significantly different (PT: 1.9 [95% CI 1.4-2.5]; FHA: 2.2 [95% CI 1.7-3.0], p<0.001). Expected infant seropositivity rates reached 80% vs 55% following second versus third trimester immunization (adjusted odds ratio [OR] 3.7 [95% CI 2.1-6.5], p<0.001).
 Early second-trimester maternal Tdap immunization significantly increased neonatal antibodies. Recommending immunization from the second trimester onwards would widen the immunization opportunity window and could improve seroprotection.

Authors:Eberhardt CS1, Blanchard-Rohner G2, Lemaître B3, Boukrid M4, Combescure C5, Othenin-Girard V4, Chilin A4, Petre J6, Martinez de Tejada B4, Siegrist CA7.
Journal:Clin Infect Dis. 2016