Invasive Haemophilus influenzae type b (Hib) infection in an adult patient with a selective deficiency of antibody to the Hib capsular polysaccharide.

A 31-year-old woman without any underlying disease contracted severe invasive Haemophilus influenzae type b (Hib) infection but developed no antibodies to the Hib capsular polysaccharide. Serum immunoglobulin levels were normal, but she had an isolated deficiency of antibody to Hib. Subsequently, immunization with a tetanus toxoid-conjugated Hib vaccine induced only a minimal response. However, she had a protective level of antibody (> 1 microgram/mL) after the fifth vaccination.