Effect of transplacentally acquired tetanus antibodies on the antibody responses to Haemophilus influenzae type b-tetanus toxoid conjugate and tetanus toxoid vaccines in Filipino infants

Background Pregnant women in developing countries are vaccinated with tetan us toroid (TT) to prevent neonatal tetanus. In populations in which the mat ernal TT-vaccination program is efficiently implemented, responses of the i nfant to TT and TT-conjugated vaccines such as Haemophilus influenzae type b (Hib) capsular polysaccaride (PS) TT-conjugate (Hib-TT) vaccine may be de pressed. Objectives. To study the influence of transplacentally acquired anti-TT ant ibodies on responses to TT vaccination and to Hib-TT vaccine. Methods. One hundred ninety-four healthy Filipino infants received three do ses of a Hib conjugate (either Hib-TT, PRP-OMP or HbOC) with diphtheria-tet anus-pertussis vaccine (DTP) given simultaneously but in a separate syringe at the age of 6, 10 and 14 weeks (primary series). In addition 54 of the s tudy children received a booster dose of Hib-TT at 9 months simultaneously with the measles vaccine. Results, Transplacentally acquired anti-TT did not interfere with the anti- Hib PS antibody (anti-Hib PS) response to any of the conjugates. The transp lacentally acquired anti TT was not significantly associated with the conce ntration of anti-Hib PS either before or after the booster dose of Hib-TT. High concentrations (greater than or equal to 1 IU/ml) of transplacentally acquired anti-TT inhibited the infants' anti-TT responses. Conclusions. High concentration of transplacentally acquired anti-TT did no t depress anti-Hib PS responses to the Hib-TT vaccine. On the other hand th e high anti-TT concentrations somewhat depressed the anti-TT responses of t he infants. However, the anti-TT concentrations attained were in the protec tive range in all study children after either the primary series (DTP + Hib -TT) or the booster dose of Hib-TT.