As late as the 1980s, serious invasive diseases caused by Haemophilus influenzae type b (Hib), chiefly meningitis and epiglottitis, were important causes of morbidity and mortality in children, especially in infants younger than 15 months. The mortality associated with Hib meningitis was 3% to 6%, and permanent neurological sequelae occurred in 20% to 30% of survivors. This degree of morbidity and mortality was comparable to that observed during the last great epidemics of paralytic poliomyelitis during the 1950s.
The first vaccines active against Hib disease were prepared from the Hib capsular polysaccharide polyribosylribitol phosphate (PRP) and introduced in the 1980s. These Hib PRP vaccines were immunogenic and clinically effective in children older than 18 months. However, they elicited little antibody response in infants aged 3 to 17 months, and two thirds of serious invasive Hib disease occurs in infants younger than 18 months. Despite this, in 1985 PRP vaccine administration
Pearson HA. Pediatrics. JAMA. 1994;271(21):1701-1703. doi:10.1001/jama.1994.03510450073041