Before 1985, Hib was the leading cause of bacterial meningitis and a common cause of other invasive diseases (such as epiglottitis, pneumonia, septic arthritis, cellulitis, purulent pericarditis, and bacteremia) among U.S. children younger than 5 years of age. An estimated 20,000 cases of invasive Hib disease occurred in this age group each year. Meningitis occurred in approximately two-thirds of children with invasive Hib disease; 15%–30% of survivors had hearing impairment or severe permanent neurologic sequelae. Approximately 4% of all cases were fatal.
Following the licensure of conjugate Hib vaccines in 1987 and 1989, the incidence of Hib disease fell dramatically. During 1989 – 2000, the annual incidence of invasive Hib disease among children younger than 5 years of age decreased by 99%, to less than one case per 100,000 children. Since 2000, the average annual incidence rate of invasive Hib disease among children younger than 5 years of age in the United States remained below the Healthy People 2020 goal of 0.27/100,000 children.
Only 18 confirmed cases of invasive Hib disease among children younger than 5 years were reported in 2019. The majority of Hib disease in the United States occurs among unimmunized and underimmunized infants and children (those who have an incomplete primary series or are lacking a booster dose) and among infants too young to have completed the primary immunization series.