A high degree of natural immunologic priming to the capsular polysaccharide may not prevent Haemophilus influenzae type b meningitis

Background. A current debate is whether the immunologic priming of infants with Haemophilus influenzae type b (Hib) conjugate vaccines would be protective in the absence of circulating antibody to the capsular polysaccharide (PS), Data from the prevaccine era on the PS antibody responses of older children to Dib meningitis may be informative on this issue. Methods, PS antibody was assayed by radioantigen binding in sera taken in the first month postadmission in 47 children ages 2 to 136 months with culture-proved Dib meningitis. Results. Sera obtained on admission had very low antibody concentrations, and the subsequent response during convalescence was age-dependent. The major finding is that some patients, including 10 of 11 children older than 2 years, had substantial antibody elevations within a few days of admission, increases resembling the response to PS vaccine in infants primed with PS-protein conjugate vaccines. Conclusions, In this group of patients with Dib meningitis, natural priming did not prevent infection. Dib may have the ability to invade despite the capacity for a vigorous antibody response.