Figure 4From: Levels of diphtheria and tetanus specific IgG of Portuguese adult women, before and after vaccination with adult type Td. Duration of immunity following vaccinationAntitetanus toxin IgG (ATT IgG) levels in pre-vaccination sera, by age at first dose of tetanus-toxoid received in women who began vaccination with TT (Group B). Regression line (stippled) and threshold level of 160 mIU/ml.Back to article page