Vaccines are one of the greatest achievements in medicine and public health, greatly reducing morbidity, mortality and health care costs. The United States and many developed nations have reduced the incidence of most vaccine preventable diseases by 98-100%. Many developing countries have also seen major accomplishments in disease prevention because of the sustained use of vaccines.

Yet, in order for vaccine programs to be effective, high rates of immunization coverage must be maintained.

Even in places like the US that have very successful immunization programs, vaccine coverage is often suboptimal in some geographic areas and sociodemographic groups.