The number of reported cases of vaccine-preventable diseases has generally decreased over the past several decades. In 2006, there were no reported cases of diphtheria or polio in the United States population, and no cases of tetanus among children under 5 years of age. Among children in this age group, there were also no reported cases of acquired rubella and only one case of congenital rubella.
From 2005 to 2006, the number of reported cases of hepatitis A and pertussis decreased among children under 5 years of age. The overall incidence of hepatitis A began dropping dramatically once routine vaccination for children living in high-risk areas was recommended beginning in 1996, and in October of 2005, the Centers for Disease Control and Prevention (CDC) instituted the recommendation that all children be immunized for hepatitis A starting at 1 year of age. The latter recommendation was made because two-thirds of cases were occurring in States where the vaccine was not currently recommended for children. With regard to pertussis, the number of cases among young children decreased by nearly 50 percent over the previous year, although the CDC reports that this is likely due to the cyclical nature of the disease and not an increase in immunization. The highest reported rate occurred among infants under 6 months of age, a population that is too young to be fully vaccinated.
While the number of reported cases of several vaccine-preventable diseases decreased between 2005 and 2006, the number of reported cases of measles and H. Influenzae increased slightly. The number of reported cases of mumps increased by a factor of 17 due to an outbreak, which was largely focused in six contiguous Midwestern States. In response, the CDC updated criteria for mumps immunity and vaccination recommendations. Reported cases of hepatitis B remained virtually unchanged.