Durability and Kinetics of Maternal Pertussis Antibodies in Infants of Mothers Immunized with Tdap During Pregnancy

BACKGROUND: Infant protection against severe pertussis requires sufficient maternal pertussis antibodies until infant immunization begins. The kinetics of maternally-derived Tdap-induced antibodies in infants is poorly understood. METHODS: 34 healthy mother-infant pairs were followed prospectively from maternal Tdap immunization to infant age 6 weeks. Blood was collected from women pre-Tdap, 4 weeks post Tdap and at delivery, and from infants at birth, and age 3 and 6 weeks. IgG to pertussis toxin (PT), filamentous hemagglutinin (FHA), fimbrial proteins (FIM) and pertactin (PRN) was quantified by luminex assay (IU/mL). Geometric mean concentrations (GMCs) with 95% confidence intervals (C.I.) for pertussis-specific IgG and half-life of IgG to PT were calculated. RESULTS: Mean maternal age was 31.1 years (range 22.7–39.7); 47% were white, 32% Hispanic and 21% Black. Tdap was administered at a mean gestation of 30.7 weeks (28–32.7). Infants had a mean gestation of 39.1 weeks (36–41.1) and birthweight of 3379g (2580–4584). GMCs (95%C.I.) for maternal pertussis-specific IgG increased significantly 4 weeks post-Tdap (4-fold higher in 59%, 41%, 29% and 44% for PT, FHA, FIM and PRN, respectively) and waned before delivery. Placental transfer was 135% for PT, 141% for FHA, 131% for FIM and 136% for PRN. Maternal antibodies in infants decayed quickly, but at age 6 weeks GMC of infant PT-specific IgG was 21.1IU/mL (14.7–30.2) and 91% had PT ≥ 10 IU/mL. Estimated half-life of PT-specific IgG in infants was 30.9 days. CONCLUSION: Although the half-life of maternal PT- specific antibodies induced by Tdap immunization during the third trimester of pregnancy is shorter than previously thought, this strategy results in levels likely sufficient to protect infants through the start of the immunization series. DISCLOSURES: All authors: No reported disclosures.