Immunoglobulin deficiency and idiotype expression in children developing Haemophilus influenzae type b disease after vaccination with conjugate vaccine

Although Haemophilus influenzae type b (Hib) vaccines are effective in preventing the disease in most children, they sometimes fails to prevent infection. When H. influenzae type b polysaccharide (Hib PS) unconjugated vaccine was licensed in 1985, the vaccine was less effective than had been expected based on a study in Finland. At the end of 1987 a conjugate vaccine (combined with a protein to enhance the immune response) combined with diphtheria toxoid (Hib PS-D) was brought to market. Although the new vaccine is highly effective, some children have developed Hib disease in spite of vaccination. To discover why this occurred, 23 patients who developed Hib disease two weeks or more after vaccination were studied. The findings were compared with those from 149 patients who became infected with Hib after vaccination with the unconjugated vaccine, and from 90 unvaccinated patients who also developed the disease. Every one of the children who developed the disease after vaccination with the Hib conjugate vaccine had abnormally low immunoglobulin (Ig) levels, specifically IgG2. From a practical standpoint, this indicates that Ig concentrations, including IgG2, should be measured in all patients, even though they do not have recurrent infections. In addition, children with deficient immune responses should be revaccinated with conjugate vaccine, because they are at increased risk of having a recurrence of the disease. Most children respond to revaccination, and those who do not should be evaluated for therapy for immunodeficiency. (Consumer Summary produced by Reliance Medical Information, Inc.)