Haemophilus influenza type b (Hib) is a bacteria responsible for severe pneumonia, meningitis and other invasive diseases almost exclusively in children aged less than 5 years.

Despite its name, it is unrelated to the influenza virus: Hib was found in a group of patients during an influenza outbreak in 1892, before scientists discovered that the flu was caused by a virus. Hib was thus proposed as the cause of influenza. Hib bacteria can cause many types of invasive disease, including meningitis, pneumonia, cellulitis (skin infection), septic arthritis (joint infection) and epiglottitis (infection of the epiglottis, causing obstruction or closing of the windpipe).

Before the Hib vaccine was introduced, meningitis—infection of the membranes that cover the brain—was the most common Hib-induced invasive disease. Symptoms include fever, stiff neck, and impaired mental status. Meningitis results in permanent hearing impairment or other neurological conditions in 15-30 per cent of patients who survive it.

It is transmitted through the respiratory tract from infected to susceptible individuals. Hib also causes potentially severe inflammatory infections of the face, mouth, blood, epiglottis, joints, heart, bones, peritoneum, and trachea. Antibiotics may be used to treat Hib infections, but the bacteria have developed resistance to some antibiotics. Hospitalization is often required.

Although this problem occurs worldwide the burden of Hib disease was considerably higher in resource-poor countries, prior to the introduction of the vaccine into their national immunization programmes. Vaccines are the only public health tool capable of preventing the majority of serious Hib disease. Hib vaccines are safe and efficacious even when administered in early infancy.

In view of their demonstrated safety and efficacy, WHO recommends the inclusion of conjugate Hib vaccines in all infant immunization programmes using any of the following schedules: three primary doses without a booster (3p+0); two primary doses plus a booster (2p+1); and three primary doses with a booster (3p+1).

The age at first dose and the number of primary doses should be set after consideration of the local epidemiology, vaccine presentation (Hib conjugate monovalent vaccine or Hib conjugate vaccine in combination with other antigens) and how this fits into the overall routine immunization schedule.