philosophical, or other nonmedical beliefs, are granted in 20 states, including Colorado and Washington, two states that saw localized outbreaks of pertussis in 2012 (Omer et al., 2006).

Although rates of medical exemptions are relatively constant nationwide, rates of nonmedical exemptions vary considerably (CDC, 2010, 2011d). For example, from 2006 to 2007, the average nonmedical exemption rate in the state of Washington was 6 percent, although some counties had exemption rates as high as 27 percent (Omer et al., 2006).

Adverse Effects of Vaccines

Parents may be what is referred to as vaccine-hesitant (refusing, delaying, or feeling unsure about some immunizations) because vaccines, like other drugs and biologicals, can in some cases be associated with adverse events (Opel et al., 2011). Vaccines that are commonly associated with serious adverse events are never licensed. Likewise, if a serious or frequent adverse event is discovered during postmarketing surveillance, the vaccine is taken off the schedule (e.g., the first rotavirus vaccine).

Most adverse events are mild or self-limited, for example, fever after measles vaccine or a sore, swollen injection site after the tetanus booster. Many events may occur in the days and weeks following vaccination, however, typically few are a result of vaccination, and most are coincidental. Ongoing research continues to examine such adverse events (IOM, 2012).

In the 1980s, the United States experienced an increase in civil lawsuits filed against vaccine manufacturers for injury compensation, which led to hesitancy on the part of the manufacturers to produce enough vaccines to keep the supply stable at a reasonable price. To streamline the legal process and maintain the vaccine supply, the U.S. Congress enacted the National Childhood Vaccine Injury Act in 1986 to establish a no-fault system for compensating individuals for vaccine-related injuries, the National Vaccine Injury Compensation Program (VICP). Individuals or parents of children who experience a vaccine-related injury must first file their petition with VICP before pursuing a civil case. As a no-fault system, the possible negligence of the manufacturer or physician is not considered in determination of compensation, which is funded by an excise tax on vaccines.

VICP covers all vaccines routinely administered to children as part of the recommended childhood immunization schedule and all injuries listed in its injury table. A claimant who seeks compensation for an adverse event that has not been established and placed in this table has the option of providing evidence to establish causation (Cook and Evans, 2011). The National Childhood Vaccine Injury Act also established the Vaccine Adverse Event Reporting System to track adverse events and created NVPO



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