PASSIVELY ACQUIRED ANTITETANUS AND ANTI-HAEMOPHILUS ANTIBODIES AND THE RESPONSE TO HAEMOPHILUS-INFLUENZAE TYPE B-TETANUS TOXOID CONJUGATE VACCINE IN INFANCY

Objective. To study the influence of maternally inherited tetanus anti toxin (anti-TT) antibodies on the response to the Haemophilus influenz ae type b (Hib) capsular polysaccharide (PS)-tetanus toroid conjugate (PRP-T) vaccine. Design. One hundred thirty healthy infants received t heir first dose of PRP-T in the same syringe with diphtheria-tetanus-p ertussis vaccine (DTP) at 1 to 2 months, and 66 of them received a sec ond dose at 3 to 4 months of age. Results. Maternal anti-TT antibodies did not interfere with the anti-Hib PS response to the first PRP-T va ccination; the geometric mean concentration (GMC) of anti-Dib PS was 0 .14 mu g/ml in those with the lowest preimmunization anti-TT (<0.3 IU/ ml, n = 15) and 0.13 mu g/ml in those with the highest anti-TT (greate r than or equal to 3 IU/ml, n = 25), After the second dose of PRP-T th ere was a positive correlation (r = 0.37, P = 0.004) between the anti- Hib PS response and the preimmunization anti-TT; those with the lowest preimmunization anti-TT (<0.3 IU/ml, n = 9) achieved GMC of anti-Hib PS of 1.22 mu g/ml and those with anti-TT greater than or equal to 3.0 IU/ml (n = 22) anti-Hib PS GMC of 2.67 mu g/ml. High preimmunization anti-Hib PS antibodies did not interfere with the final antibody conce ntrations; the GMC of anti-sib PS after the second dose of PRP-T was 1 .60 mu g/ml in those with a preimmunization titer greater than or equa l to 1.0 mu g/ml (n = 12) and 1.57 mu g/ml in those with a titer of <1 .0 mu g/ml (n = 53). Conclusion. The data suggest that infants can be safely vaccinated with PRP-T even though they have received high conce ntrations of anti-TT from their mother.