"There are several strains of Haemophilus Influenza. Haemophilus Influenza b is an extremely rare mutant strain of the normal flora that lives in the nose and throat. Most cases of Haemophilus Influenza colonization do not cause disease. Prior to the introduction of the Hib vaccine, most children acquired natural immunity by the time they were 6 years old. Hib must enter into the bloodstream for it to cause meningitis or other forms of invasive disease."