Effect of previous infection on antibody response of children to vaccination with capsular polysaccharide of Haemophilus influenzae Type b.

Children who had recovered from meningitis, orbital cellulitis, or epiglottitis caused by Haemophilus influenzae type b were immunized with capsular polysaccharide vaccine derived from that bacterium; some healthy siblings and adults who had not had H. influenzae infections were also vaccinated. Of 10 children who had had H. influenzae meningitis previously, only one had an antibody response to the vaccine. One child with prior H. influenzae orbital cellulitis also failed to respond. None of the children had detectable H. influenzae polysaccharide antigen in their bloodstream at the time of immunization. Two children who had had H. influenzae epiglottitis and six of seven controls without histories of H. influenzae infections responded immunologically to the vaccine. One of eight vaccinees under two years of age showed a response, and eight of 12 over two years responded well (P = 0.02). All four nonresponders over the age of two years had had H; influenzae meningitis or cellulitis. Children who had had H. influenzae meningitis responded less well to the polysaccharide vaccine than did other recipients of the vaccine; this difference could not be explained solely on the basis of age;