Methods: Avidity of anti-PTIgG was assessed using ammonium thiocyanate (NH4SCN) at concentrations between 0.25M (to measure low avidity antibodies) and 3M (to measure high avidity antibodies). Anti-PT IgG levels achieved at each NH4SCNconcentration were calculated. T-tests were used to compare anti-PT IgG levels between newborns of women vaccinated in early (28-32 weeks gestation [WG]) and late (33-36 WG) 3rdtrimester. Pearson correlation assessed the relationship between the timing of vaccination and anti-PT IgG levels.
Results: Newborns of women vaccinated with Tdap in early 3rdtrimester (n=43) had higher anti-PT IgG levels at 1M and 2M NH4SCNconcentrations compared with newborns of women vaccinated in late 3rdtrimester (n=47), 2.4 international units (IU)/ml vs. 1.9 IU/ml (p=0.0073) and 2.3 IU/ml vs. 1.7 IU/ml (p=0.0354), respectively, after adjustment for gestational age at birth. There was a negative association between later timing of vaccination in 3rdtrimester and anti-PT IgG levels achieved at 0.5M, 1M, 1.5M, and 2M NH4SCN(all p≤0.02).There was a positive association between increasing time between vaccination and delivery and anti-PT IgG levels achieved at0.5M, 1M, 1.5M and 2M NH4SCN(all p≤0.02).
Conclusion: Vaccination against pertussis during early 3rdtrimester results in higher levels of high avidity antibodies compared with vaccination in late 3rdtrimester. High avidity antibodies may confer greater protection to the neonate supporting recommendations for vaccination at 28-32 WG vs. 33-36 WG.
B. Abu Raya,
T. Kollmann, None
M. Sadarangani, None