, according to a prospective cohort study published in Obstetrics and Gynecology.
Timing does make a difference with the other Tdap option in pregnancy, Boostrix; pertussis protection is stronger if women receive it early in the third trimester. The investigators wanted to see if that were true as well with Adacel.
They compared pertussis antibody concentrations in maternal venous serum and umbilical cord arterial serum at the time of delivery in 52 women vaccinated from 27 to 30 6/7 weeks of gestation, and compared the results with 36 women vaccinated from 31 to 35 6/7 weeks.
Pertussis antibody concentrations did not vary by gestational age. Maternal serum pertussis toxin IgG concentrations were the same in both groups (48.6 enzyme-linked immunoassay [ELISA] units/mL), and there were no statistically significant differences in cord serum pertussis toxin IgG concentrations (92.1 ELISA units/mL in the early group, compared with 90.7 in the later group; P = .95) or cord serum pertactin IgG concentrations (798 international units/mL in the early group, versus 730 in the later group; P = .73).
Overall, cord serum pertussis toxin IgG concentrations were approximately twice maternal serum pertussis toxin IgG concentrations (91.6 vs. 48.6 ELISA units/mL; P less than .01). Cord serum pertussis toxin IgG concentrations were in the protective range (greater than 10 ELISA units/mL) in 87% of the women vaccinated from 27 to 30 6/7 weeks, and in 97% vaccinated from 31 to 35 6/7 weeks (P = .13).
Maternal vaccination in the third trimester against pertussis “was associated with a high percentage of newborns with antibody concentrations conferring protection,” said investigators led by Cynthia Abraham, MD, an ob.gyn. at Mount Sinai Hospital, New York. “We found no significant difference across the period of 27-36 weeks of gestation with respect to immunogenicity with Adacel use.”
Maternal Tdap vaccination is done to protect infants in their first 2 months of life, before they start their DTaP series. The Centers for Disease Control and Prevention recommends vaccination between 27 and 36 weeks of gestation.
It’s unclear why it doesn’t matter when within that window women receive Adacel, but protection with Boostrix if Boostrix is administered early on in the trimester.
Boostrix differs from Adacel in antigen composition and in the method of pertussis toxin detoxification. Boostrix is detoxified with formaldehyde and glutaraldehyde. Adacel is detoxified only with formaldehyde.
“Double detoxification may cause differences in immunogenicity as antigenic epitopes are further modified, perhaps providing an explanation for the difference in results between the vaccines,” the investigators said.
Women in the early group received Adacel at a mean gestational age of 29.1 weeks, versus 32.9 weeks in the later group. The women were a mean age of about 29 years; 56% were Hispanic, 23% white, and the rest were about equally split between black and Asian women.
No funding source was reported. The authors did not have any conflicts of interest.
SOURCE: Abraham C et al. Obstet Gynecol. 2018 Feb;131(2):364-9.