The CDC estimates that before the Hib ( Haemophilus influenzae type b) vaccine was licensed in 1985, each year about 20,000 children in the U.S. developed Hib disease, and about 500 children died of it. Nearly all of these patients were younger than 5 years old. Many of those who survived were left blind, deaf, learning disabled, or permanently brain damaged. In fact, before the vaccine, this disease caused the most common form of mental retardation acquired after birth.

Hib vaccine began to be used in the late 1980s. By 1998, only 228 children caught Hib disease, a decline of almost 99 percent.

Despite its name, Haemophilus influenzae type b is not related to influenza. The doctor who named the disease in the late 1800s confused it with the influenza that his patient also had. The real nature of Hib was not clarified until the 1930s.

Because Hib often causes a form of meningitis, its vaccine has been called "the meningitis vaccine." But meningitis has many different causes and forms.