NCPA - National Center for Policy Analysis


May 11, 2009

Vaccines are among the most effective prevention tools available to clinicians.  However, the success of an immunization program depends on high rates of acceptance and coverage.  There is evidence of an increase in vaccine refusal in the United States and of geographic clustering of refusals that results in outbreaks, according to a new study by the New England Journal of Medicine.

All states require that children receive vaccinations, but 21 states allow parents to exempt their children for personal reasons.  Some parents fear side effects from vaccinations and believe that mercury, previously used as a preservative in vaccines, is responsible for an increase in autism diagnoses, according to the study.  However, lead author Saad Omer of Emory University said there is no evidence to support these fears.

  • According to Centers for Disease Control (CDC), about 2.8 percent of children in these states were not vaccinated in 2008 because of parents' beliefs, up from 1 percent in 1999.
  • The outbreaks of diseases, such as measles and whooping cough, are growing in these states.

Lance Rodewald, immunization director for CDC, said that while routine coverage for such illnesses has never been at a higher level nationwide, local clusters of unvaccinated youths are a growing concern.  While vaccines for diseases such as whooping cough cannot completely eliminate risk of contagion and some children cannot be vaccinated for medical reasons, health officials aim to vaccinate a large percentage of a population to keep infections from spreading, a tactic they call "herd immunity." 

Many schools with high numbers of children whose parents have elected to forgo vaccinations have been linked to outbreaks:

  • For example, during the period from 2006 through 2007, the state-level nonmedical-exemption rate in Washington was 6 percent, however, the county-level rate ranged from 1.2 to 26.9 percent.
  • In a spatial analysis of Michigan's exemption data according to census tracts, 23 statistically significant clusters of increased exemptions were identified.
  • Similar heterogeneity in exemption rates has been identified in Oregon27 and California (unpublished data).

"People need to recognize that in the case of infectious diseases, what other people do impacts my child.  If they live in a community that has a cluster of refusers, their risk of getting a vaccine-preventable disease goes up, just by virtue of who they play with," says Omer.

Source: Saad B. Omber et al., "Vaccine Refusal, Mandatory Immunization and the Risks of Vaccine-Preventable Diseases," New England Journal of Medicine, Vol. 360, No. 19, May 7, 2009.

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