CIAO3 and pertussis: However, after primary vaccination, anti-PT and anti-PRN did not show statistical differences between the Tdap group and the control group, and GMCs of anti-FHA were statistically less in the Tdap group than the control group, suggesting that maternal immunization with Tdap resulted in high concentrations of pertussis antibodies in infants during the first 2 months of life until they get primary vaccinated.