Comparison of active and combined passive/ active immunization of navajo children against haemophilus influenzae type b

In a high risk Navajo population we compared the immunogenicity of a new Haemophilus influenzae type b mutant-diphtheria toxic conjugate vaccine (HbOC) with simultaneous active (HbOC) and passive immunization with bacterial polysaccharide immunoglobulin prepared from adults immunized with H. influenzae b, pneumococcal and meningococcal vaccines. Only 7 of 26 (27%) 2-month-olds had an increase in H. influenzae b capsular polysaccharide antibody after a single dose of HbOC, a proportion similar to that of saline controls (9 of 25, 36%). After a second HbOC dose at 4 months 88% had antibody concentrations of 0.15 mUg or more, and after a third dose at 6 months all had antibody levels ⩽0.15 Mg/ml. The group receiving both HbOC and bacterial polysaccharide immunoglobulin at 2 months uniformly had H. influenzae b CP antibody concentrations of ⩽0.15 mUg/ml at 4 months (P < 0.001 relative to “HbOC alone” group) and subsequently responded similarly to second and third doses of HbOC vaccine as did also the “HbOC alone” group. We conclude that combined passive/active immunization with bacterial polysaccharide immunoglobulin and HbOC at 2 months maintains antibody at concentrations thought to be protective (⩽0.15 mUg/ml) without interfering with the active antibody response to second and third doses of HbOC at 4 and 6 months of age.