NEONATAL IMMUNIZATION - RESPONSE TO HAEMOPHILUS-INFLUENZAE TYPE B-TETANUS TOXOID CONJUGATE VACCINE

Objective. To study the immunogenicity and tolerability of Haemophilus influenzae type b (Hib) conjugate vaccine administered in the neonata l period. Design. Hib capsular polysaccharide (PS)-tetanus toroid conj ugate vaccine (PRP-T) was given to 120 neonates at 2 days of age, foll owed by PRF-T or the Hib PS vaccine at 4 months and a PRP-T booster at 14 months. Their anti-Hib PS concentrations were compared with those in children receiving PRP-T at 2 and 4 months or at 4 months. Results. No serious adverse reactions were noted. The geometric mean concentra tion of anti-Hib PS at the age of 2 days was 0.34 mu g/mL and at 4 mon ths was 0.12 mu g/mL. This was significantly more than the concentrati on in unimmunized infants at this age and 3.5 times more than expected , taking into account the natural decay of transplacentally acquired a ntibodies. Such a response was not seen in infants with a high (greate r than 3.0 mu g/mL) neonatal antibody concentration. The PRP-T vaccine given at 4 months elicited an antibody response in all infants and Hi b PS in 62%, indicating immunologic priming. At 14 months a higher per centage of the infants who had received PRP-T at 2 days and 4 months t han of those who had received PRP-T at 4 months only had anti-Hib PS c oncentrations greater than 0.15 mu g/mL. All infants responded well to the booster at 14 months. There was no evidence of immunologic tolera nce. Conclusions. Neonatal immunization with PRP-T was safe and well t olerated in Finnish infants, and it would be worthwhile to further stu dy its effects in higher risk populations.