This study evaluated the seroprevalence of Bordetella pertussis antibodies and anti-pertussis antibody response after a single dose of reduced-antigen, combined diphtheria, tetanus, and acellular pertussis vaccine (Tdap) in pregnant Thai women.

All seronegative participants received Tdap, while seropositive participants were equally randomized into 2 groups. Half of seropositive participants received Tdap and the other half received tetanus-diphtheria (Td) as standard protocol.

The primary objective of this study was to determine the seroprevalence of anti-pertussis toxin antibodies (anti-PT IgG) among pregnant Thai women. The secondary objectives were to evaluate antibody response after Tdap vaccination between seronegative and seropositive participants and to compare the different antibody titers at delivery among seropositive participants who received Tdap to those who received tetanus-diphtheria vaccine (Td). The sample size calculation was based on the primary objective. Randomized clinical trial was performed for the latter secondary objective.

Inclusion Criteria:

• Thai pregnant women age at least 18 years
• No known underlying disease
• Singleton pregnancy without maternal or fetal complications
• Gestational age not more than 20 weeks at the time of recruitment
• Desired for delivery at Siriraj Hospital

Exclusion Criteria:

• Pregnant women who have any contraindication to Tdap vaccine including

  1. History of serious allergic reaction to any components of Tdap vaccine
  2. History of seizure or coma after receiving Tdap vaccine in childhood
  3. Having an underlying disease involving central nervous system (e.g., epilepsy, Guillain-Barré syndrome)

• History of serious reactions after receiving Tdap vaccine (e.g., severe pain, severe swelling at the injection site)

• Recently had Tdap vaccine injection

• Denied for Tdap vaccine injection

Through study completion, an average of 11 months