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
Phase: EARLY_PHASE1
Conditions: Pertussis, Pregnancy Related
Sponsor: Mahidol University

 
Seroprevalence of Bordetella pertussis antibodies and anti-pertussis antibody 
response after a single dose of Tdap in pregnant Thai women  
NCT number: NCT 03498300  
Document date: March 11, 2020 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

Background: Maternal immunization with tetanus toxoid, reduced diphtheria toxoid, and acellular 
pertussis vaccine (Tdap) has recently been implemented to prevent infant pertussis. Tdap is still 
not routinely recommended in Thailand, and there are limited data to support or challenge this 
strategy. 
Objectives:  The primary aim was to determine the seroprevalence of anti- pertussis toxin 
antibodies (anti-PT IgG) among pregnant Thai women. The secondary aims were to evaluate 
antibodies response after Tdap vaccination between seronegative and seropositive mothers and to 
compare the different antibody titers at delivery among seropositive mothers who received Tdap 
to those who received tetanus-diphtheria vaccine (Td). 
Methods: This randomized clinical trial was conducted during April 2018 to April 2019 at Siriraj 
Hospital, Bangkok, Thailand. A total of 129 pregnant women were included. Paired blood samples 
for anti-PT IgG levels were obtained during the first antenatal visit and at delivery. A baseline cut-
off value of <5 IU/ml indicated seronegativity. All seronegative participants (n=69) received Tdap, 
while the seropositive group were randomized 1:1 to receive either Tdap (n=18) or Td (n=13) 
during 27-36 weeks’ gestation. The antibody levels from both sera were compared between groups. 
Statistical analysis: All data analyses were performed using PASW Statistics version 18.0 for 
Windows (SPSS, Inc., Chicago, IL, USA). Descriptive data are presented as number and 
percentage, mean ± standard deviation, or median and range (minimum–maximum), as 
appropriate. One-way analysis of variance (ANOVA) and Kruskal-Wallis test was used to compare 
continuous variables with and without normal distribution among 3 groups, respectively. Either 
Pearson’s chi-square test or Fisher’s exact test was used to compare qualitative characteristics 
among groups. Comparison of anti-PT IgG levels between the first antenatal care (ANC) and 
during delivery in each group was performed using Wilcoxon test. Mann-Whitney U test was used 
to evaluate antibody response after Tdap vaccination between seronegative and seropositive 
mothers (group 1 vs. group 2), and to compare the different anti-PT IgG levels of paired serum 
samples among seropositive mothers between those who received Tdap and those who received 
Td (group 2 vs. group 3). Spearman’s rho analyses were performed to examine the correlation of 
the increment of anti-PT IgG titers with the interval of Tdap vaccination and delivery. A p-value 
<0.05 was considered statistically significant.