Background: Center for Disease Control and Prevention recommends vaccination of pregnant women with tetanus-diphtheria-acellular pertussis (Tdap).

Aim: To measure pertussis specific antibodies, total protein and their ratio in breast milk following gestational Tdap vaccination.

Methods: Women who received Tdap after the 20th week of pregnancy were recruited and unvaccinated women served as controls. Breast milk total protein, immunoglobulin A (IgA) to pertussis toxin (PT), filamentous hemagglutinin (FHA) and immunoglobulin G (IgG) to PT, FHA and pertactin (PRN) were measured. To overcome the dilution that occurs in the transition from colostrum to mature breast milk, we calculated pertussis specific antibody to total protein ratio.

Results: Pertussis specific IgA was the predominant pertussis immunoglobulin in the colostrum of Tdap vaccinated women with the geometric mean concentrations (GMCs) of IgA to FHA higher than for IgA to PT, 24.12 ELISA units/milliliter (EU/mL) vs. 8.18EU/mL, respectively, p<0.004. There were differences between the vaccinated women and controls in the GMCs of IgA to FHA and IgG to PRN in the colostrum, 24.12EU/mL vs. 6.52EU/mL, p=0.01 and 2.46EU/mL vs. <0.6EU/mL, p=0.03, respectively. The GMCs of total protein showed significant decline over 8 weeks in the vaccinated women and controls, p<0.004. Among vaccinated women, there was significant decline in the GMCs of IgA to PT and FHA over 8 weeks, p<0.001. The geometric mean ratio of IgA to FHA to total protein also declined significantly over 8 weeks in the vaccinated women, p<0.01, demonstrating a true decrease, however, pertussis IgA was measurable at 8 weeks.

Conclusions: Select colostrum pertussis antibody levels were significantly higher among women vaccinated with Tdap during pregnancy compared with unvaccinated women. Among vaccinated women, maximal levels of pertussis specific IgA were in the colostrum but still detected at 8 weeks. Lactation may augment infant's protection against pertussis.