Figure 2.

Fractional absolute anti-PT IgG levels by time elapsed from vaccination against pertussis in pregnancy to delivery achieved at the different ammonium thiocyanate concentrations. The quantified fractional absolute avidity levels of anti-PT IgG at 0.25 molar (M), 0.5, 1, 1.5, 2, and 3 M of ammonium thiocyanate are classified as low (A), low-medium (B), medium (C), medium-high (D), high (E), and very high (F) avidity anti-PT IgG antibodies, respectively. The horizontal line denotes the cord mean levels in newborns born to unvaccinated women. PT, pertussis toxin; IU/ml, international unit/ml. This figure shows that the longer the interval between Tdap administration during the third trimester and delivery, the higher the fractional absolute levels of low–medium, medium, medium–high, and high avidity anti-PT IgG achieved at birth.