component of vaccines (not including influenza and hepatitis A virus vaccines) by age 3 years. According to the National Immunization Survey (NIS), less than 1 percent of U.S. children aged 19 to 35 months receive no vaccinations at all (CDC, 2011c). However, not every vaccine on the schedule has equal coverage in this population. In the NIS study population for children born between January 2008 and May 2010, vaccines with higher coverage included the poliovirus vaccine (93.9 percent), MMR (91.6 percent), the hepatitis B vaccine (91.1 percent), and the varicella vaccine (90.8 percent). In contrast, the rotavirus vaccine was received by only 67.3 percent of children, and just 80.7 percent of children received the full series of the Hib vaccine, which is an increase from previous years during which a shortage of the vaccine was experienced (CDC, 2012a). A review of data from the 2003 NIS revealed that more than one in three children were undervaccinated (missing age-appropriate doses from the recommended immunization schedule) during the first 24 months of life and that only 18 percent of U.S. children received all vaccinations at the recommended times or acceptably early (Luman et al., 2005). Immunizations are recommended to protect children when they are most vulnerable to vaccine-preventable diseases, and delays in timely immunization leave children susceptible to disease.
For some children, vaccination on the recommended schedule may be contraindicated, either permanently or temporarily, and the CDC offers guidelines on conditions that may require that vaccination with certain vaccines be postponed or avoided altogether (CDC, 2011b).
Most health care providers encourage adherence with the recommended immunization schedule for children; however, a compelling motivator to see that children receive their full immunizations is their requirement to attend school. Since the early 1980s, all 50 states have made policy decisions to require immunizations for school entry. These immunization requirements were originally enacted to prevent and control frequent outbreaks of vaccine-preventable diseases. Furthermore, during outbreaks, officials have removed unvaccinated children from school, which has proved to be a successful control measure (Omer et al., 2006).
Because school-based immunization requirements are determined on a state-by-state basis, differences in age requirements, processes for adding new vaccines, and exemptions to immunizations exist across the country. Exemptions may be medical in nature, such as exemptions for delayed or skipped immunization if the child has a condition that contraindicates immunization with the vaccine, as referenced above.
Currently, every state law covering immunization requirements has a provision that allows medical exemptions. Parents may also request an exemption on religious grounds, and such exemptions are permitted in 48 states. Exemptions because of personal beliefs, which include religious,