Haemophilus influenza (which includes Haemophilus influenza type B, or Hib), according to the CDC, is "a bacterium that can cause severe infection, occurring mostly in infants and children younger than five years of age. In spite of its name, Haemophilus influenza does not cause influenza (the 'flu'). It can cause lifelong disability and be deadly."
In 1892, Richard Pfeiffer, a German physicist, isolated a bacterium from the lungs of flu patients that would be called "Pfeiffer influenza bacillus" in 1896 by Karl Lehmann and Rudolf Neuman in Atlas and Principles of Bacteriology. The bacterium was assumed to cause influenza. In the 1930s, researchers established that influenza was caused by a virus and not a bacterium so "Pfeiffer influenza bacillus" was renamed Haemophilus influenzae type B (Hib) as a nod to the incorrect association with the flu. In 1931, Margaret Pittman, PhD, an American researcher, linked Hib to meningitis. Later it would be confirmed that Hib can cause other serious diseases including infections of the skin, blood, bones, and joints; pneumonia; and epiglottitis. Work on an Hib vaccine began in 1968 by Porter W. Anderson, Jr., PhD, and David Smith, MD, which lead to a 1975 trial that showed the vaccine worked in infants but not toddlers. Smith founded a company to produce the vaccine when it was licensed in 1985 because no existing pharmaceutical company wanted to manufacture it. This HbPV polysaccharide vaccine was used until 1988. As of July 24, 2014, there are six Hib vaccines on the market (three for Hib only; one Hib/Hep B combination; one DTaP-IPV/Hib combination; and one meningococcal vaccine).
Below are three graphs. The first shows the number of Hib cases in the United States, adults and children, from 1972 to 2013. The second graph shows the number of deaths caused by the Hib bacterium in adults and children from 1972 to 2013. And the third graph shows the Hib vaccination rates among children aged 19 to 36 months in the United States since Varivax was licensed for use.
As of Aug. 18, 2014, the CDC recommends that children receive the first dose of Hib vaccination at two months of age.
Microscopic view of the Hib bacterium Source: Sanofi Pasteur, "Haemophilus Influenzae Type B," www.flickr.com, Aug. 7, 2013