Hib disease is a serious illness caused by the bacteria Haemophilus influenzae type b. Babies and children younger than 5 years old are most at risk for Hib disease, but it can also affect adults with certain medical conditions.

Hib bacteria can cause mild illness, such as ear infections or bronchitis, or they can cause severe illness, such as infections of the bloodstream. Hib disease can cause lifelong disability and be deadly.

The Hib vaccine prevents Hib disease. Depending on the brand of the Hib vaccine, three or four doses are recommended. Infants will usually get their first dose of Hib vaccine at age 2 months, and will usually complete the series by the time they are 12- to 15-months old.

According to the Centers for Disease Control and Prevention (CDC), before Hib vaccine, Hib disease was the leading cause of bacterial meningitis among children under age 5 years in the US.