VACCINE

Vaccine Refusal, Mandatory Immunization, and the Risks of Vaccine-Preventable Diseases  

Vaccines are among the most effective
  tools available for preventing infectious diseases and their complications and sequelae. High immunization coverage has resulted in drastic declines in vaccine-preventable diseases, particularly in many high- and middle-income countries. A reduction in the incidence of a vaccine-preventable disease often leads to the public perception that the severity of the disease and susceptibility to it have decreased.1 At the same time, public concern about real or perceived adverse events associated with vaccines has increased. This heightened level of concern often results in an increase in the number of people refusing vaccines.1,2
In the United States, policy interventions, such as immunization requirements for school entry, have contributed to high vaccine coverage and record or near-record lows in the levels of vaccine-preventable diseases. Herd immunity, induced by high vaccination rates, has played an important role in greatly reducing or eliminating continual endemic transmission of a number of diseases, thereby benefiting the community overall in addition to the individual vaccinated person.
Recent parental concerns about perceived vaccine safety issues, such as a purported association between vaccines and autism, though not supported by a credible body of scientific evidence,3-8 have led increasing numbers of parents to refuse or delay vaccination for their children.9,10 The primary measure of vaccine refusal in the United States is the proportion of children who are exempted from school immunization requirements for nonmedical reasons. There has been an increase in state-level rates of nonmedical exemptions from immunization requirements.11 In this article, we review the evidentiary basis for school immunization requirements, explore the determinants of vaccine refusal, and discuss the individual and community risks of vaccine-preventable diseases associated with vaccine refusal.

Evolution of U.S. Immunization Requirements

Vaccination was introduced in the United States at the turn of the 19th century. The first U.S. law to require smallpox vaccination was passed soon afterward, in 1809 in Massachusetts, to prevent and control frequent smallpox outbreaks that had substantial health and economic consequences.12-14 Subsequently, other states enacted similar legislation.13 Despite the challenges inherent in establishing a reliable and safe vaccine delivery system, vaccination became widely accepted as an effective tool for preventing smallpox through the middle of the 19th century, and the incidence of smallpox declined between 1802 and 1840.15 In the 1850s, “irregular physicians, the advocates of unorthodox medical theories,”16 led challenges to vaccination. Vaccine use decreased, and smallpox made a major reappearance in the 1870s.15 Many states passed new vaccination laws, whereas other states started enforcing existing laws. Increased enforcement of the laws often resulted in increased opposition to vaccination. Several states, including California, Illinois, Indiana, Minnesota, Utah, West Virginia, and Wisconsin, repealed compulsory vaccination laws.15 Many other states retained them.
In a 1905 landmark case, Jacobson v. Massachusetts, which has since served as the foundation for public health laws, the U.S. Supreme Court endorsed the rights of states to pass and enforce compulsory vaccination laws.17 In 1922, deciding a case filed by a girl excluded from a public school (and later a private school) in San Antonio, Texas, the Supreme Court found school immunization requirements to be constitutional.18 Since then, courts have been generally supportive of the states' power to enact and implement immunization requirements.
Difficulties with efforts to control measles in the 1960s and 1970s ushered in the modern era of immunization laws in the United States.12 In 1969, a total of 17 states had laws that required children to be vaccinated against measles before entering school, and 12 states had legally mandated requirements for vaccination against all six diseases for which routine immunization was carried out at the time.13 During the 1970s, efforts were made to strengthen and strictly enforce immunization laws.12,13 During measles outbreaks, some state and local health officials excluded from school those students who did not comply with immunization requirements, resulting in minimal backlash, quick improvement in local coverage, and control of outbreaks.19-22 Efforts by the public health community and other immunization advocates to increase measles vaccine coverage among school-age children resulted in enforcement of immunization requirements for all vaccines and the introduction of such requirements in states that did not already have them. By the beginning of the 1980s, all 50 states had school immunization requirements.

Recent School Immunization Requirements  

Because laws concerning immunization are state-based, there are substantial differences in requirements across the country. The requirements from state to state differ in terms of the school grades covered, the vaccines included, the processes and authority used to introduce new vaccines, reasons for exemptions (medical reasons, religious reasons, philosophical or personal beliefs), and the procedures for granting exemptions.23
State immunization laws contain provisions for certain exemptions. As of March 2008, all states permitted medical exemptions from school immunization requirements, 48 states allowed religious exemptions, and 21 states allowed exemptions based on philosophical or personal beliefs.23 Several states (New York, Arkansas, and Texas) have recently expanded eligibility for exemptions.

Secular and Geographic Trends in Immunization Refusal

Between 1991 and 2004, the mean state-level rate of nonmedical exemptions increased from 0.98 to 1.48%. The increase in exemption rates was not uniform.11 Exemption rates for states that allowed only religious exemptions remained at approximately 1% between 1991 and 2004; however, in states that allowed exemptions for philosophical or personal beliefs, the mean exemption rate increased from 0.99 to 2.54%.11
Like any average, the mean exemption rate presents only part of the picture, since geographic clustering of nonmedical exemptions can result in local accumulation of a critical mass of susceptible children that increases the risk of outbreaks. There is evidence of substantial geographic heterogeneity in nonmedical-exemption rates between and within states.24 For example, in the period from 2006 through 2007, the state-level nonmedical-exemption rate in Washington was 6%; however, the county-level rate ranged from 1.2 to 26.9% (Figure 1Figure 1Rates of Exemption from Vaccination for Nonmedical Reasons in Washington Counties, 2006–2007.).25 In a spatial analysis of Michigan's exemption data according to census tracts, 23 statistically significant clusters of increased exemptions were identified.26 Similar heterogeneity in exemption rates has been identified in Oregon27 and California (unpublished data).
The reasons for the geographic clustering of exemptions from school vaccination requirements are not fully understood, but they may include characteristics of the local population (e.g., cultural issues, socioeconomic status, or educational level), the beliefs of local health care providers and opinion leaders (e.g., clergy and politicians), and local media coverage. The factors known to be associated with exemption rates are heterogeneity in school policies28 and the beliefs of school personnel who are responsible for compliance with the immunization requirements.29
Instead of refusing vaccines, some parents delay vaccination of their children.30-32 Many parents follow novel vaccine schedules proposed by individual physicians (rather than those developed by expert committees with members representing multiple disciplines).32,33 Most novel schedules involve administering vaccines over a longer period than that recommended by the Advisory Committee on Immunization Practices and the American Academy of Pediatrics or skipping the administration of some vaccines.