Invasive disease caused by Hemophilus influenzae type b (HIB) is recognized as a leading pediatric health problem. This agent is the leading cause of bacterial meningitis in the United States and, in addition, causes a wide variety of other serious infections. It is estimated that approximately 20,000 cases of invasive HIB disease occur annually in the United States, affecting one in every 200 children during the first five years of life. This incidence exceeds that of meningococcal disease by several fold and is similar to the peak incidence of paralytic poliomyelitis during the early 1950s. Furthermore, despite the availability of effective antimicrobials, significant morbidity, especially postmeningitic sequelae, and mortality continue. Consequently, there is no debate about the need for an effective vaccine, especially for young infants who are at greatest risk.
It has been known for many years that antibody to the capsular polysaccharide of HIB, polyribosylribitol-phosphate (PRP), is protective