1. clinical experience and observations, observational studies with important limitations, or randomized controlled trials with several major limitations.

Recommendations from ACIP are also categorized into Category A or B recommendations, although the distinction does not reflect the quality of the evidence reviewed. Category A recommends vaccination for all people in a particular age group or for a group at increased risk for vaccine-preventable diseases. Category B recommendations do not apply to all members of a group; rather, they are intended to provide guidance to a clinician when determining if vaccination is appropriate for an individual. After review, if CDC accepts the recommendations of ACIP, they are published in Morbidity and Mortality Weekly Reports (MMWR) (Smith, 2010; Smith et al., 2009).

PAST AND PRESENT IMMUNIZATION SCHEDULES

The current schedule of recommended immunizations for infants and children from birth through age 6 years comprises vaccines that prevent 14 infectious diseases, a remarkable achievement compared with the schedule in 1948, when immunizations against only diphtheria, tetanus, pertussis, and smallpox were available and recommended for administration for protection. In 1955, the polio vaccine was licensed and added to the recommended immunizations to eliminate yearly outbreaks. Over the next 40 years, vaccines were added to the recommended schedule as they were licensed, including MMR, the hepatitis B vaccine, and the Haemophilus influenzae type b vaccine (Hib). Smallpox vaccine was removed from the U.S. recommended schedule in 1972, as the disease had been eliminated as a result of great public health efforts.

It became increasingly evident that as the schedule became more complex, providers would benefit from annual updates with detailed information about new vaccines, who should receive each vaccine, the age(s) at the time of receipt, the dose, and the use of combination vaccines in their practices. In 1995, CDC, AAP, and AAFP created a harmonized immunization schedule. Since then, the ACIP-recommended schedule has been adopted by the CDC and both professional associations, along with others (CDC, 2012c). Today, combination vaccines deliver immunizations against up to five separate diseases in a single injection, including DTaP-Hib-inactivated poliovirus vaccine (IPV) and DTaP-hepatitis B (recombinant) virus vaccine-IPV.

Immunization rates for children in the United States are generally high, with some variation occurring depending on geography and the specific vaccine. The majority of children are fully immunized with the recommended



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