Before Hib immunizations became available, Hib was the most common cause of bacterial meningitis in US infants and children. Before the vaccine was developed, there were approximately 20,000 invasive Hib cases annually. Approximately two thirds of the annual cases were meningitis. Up to 8,000 additional cases of life-threatening invasive Hib disease - bacteremia, pneumonia, or epiglottitis - also occurred annually. One of every 200 US children under 5 years of age got Hib disease. Hib meningitis killed 600 children each year, and left many survivors with deafness, seizures, or mental retardation.

Since the introduction of conjugate Hib vaccine in December 1987, the incidence of Hib has declined by 97% to 99%. Fewer than 10 fatal cases of invasive Hib disease were reported in 1995.

This preventable disease was still a common, devastating illness as recently as 1990; now, most pediatricians just finishing training have never seen a case. If we were to discontinue immunization, we would likely soon return to the pre-vaccine numbers of invasive Hib disease cases and deaths.