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.

Abstract

Pregnant women in developing countries are vaccinated with tetanus toxoid (TT) to prevent neonatal tetanus. In populations in which the maternal TT-vaccination program is efficiently implemented, responses of the infant to TT and TT-conjugated vaccines such as Haemophilus influenzae type b (Hib) capsular polysaccaride (PS) TT-conjugate (Hib-TT) vaccine may be depressed. To study the influence of transplacentally acquired anti-TT antibodies on responses to TT vaccination and to Hib-TT vaccine. One hundred ninety-four healthy Filipino infants received three doses of a Hib conjugate (either Hib-TT, PRP-OMP or HbOC) with diphtheria-tetanus-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 study children received a booster dose of Hib-TT at 9 months simultaneously with the measles vaccine. Transplacentally acquired anti-TT did not interfere with the anti-Hib PS antibody (anti-Hib PS) response to any of the conjugates. The transplacentally acquired anti-TT was not significantly associated with the concentration of anti-Hib PS either before or after the booster dose of Hib-TT. High concentrations (> or =1 IU/ml) of transplacentally acquired anti-TT inhibited the infants' anti-TT responses. High concentration of transplacentally acquired anti-TT did not depress anti-Hib PS responses to the Hib-TT vaccine. On the other hand the high anti-TT concentrations somewhat depressed the anti-TT responses of the infants. However, the anti-TT concentrations attained were in the protective range in all study children after either the primary series (DTP + Hib-TT) or the booster dose of Hib-TT.