Until recently, Hib was one of the most important causes of bacterial infection in young children. Hib may cause a variety of diseases such as meningitis (inflammation of the coverings of the spinal column and brain) , blood stream infections, pneumonia, arthritis and infections of other parts of the body.
Due to routine use of the Hib conjugate vaccine since 1990, the incidence of Hib disease in infants and young children has decreased by 99% to fewer than 1 case per 100,000 children under 5 years of age. In the United States, Hib disease occurs primarily in underimmunized children and among infants too young to have completed the primary immunization series. In developing countries, where routine vaccination with Hib vaccine is not widely available, Hib remains a major cause of lower respiratory tract infections in infants and children.