CDC: With low vaccine rates, some areas risk losing herd immunity

Certain communities face an increased risk of infection due to opt outs

A new CDC report shows that the vaccination rate for kindergarteners in the 2013-2014 school year varied among states, with rates low enough in some areas to put communities at risk of losing herd immunity.

To maintain herd immunity, communities have to vaccinate enough residents to protect the small number of people who cannot receive a vaccination for medical reasons. For example, medical experts say that between 92% and 95% of children should receive two doses of the measles, mumps, and rubella (MMR) vaccine to maintain herd immunity against measles.

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For the report, CDC examined vaccination data from Washington, D.C., and all states except Wyoming, which did not provide the information. CDC also assessed vaccination rate exemption data from 46 reporting states and Washington, D.C.

National findings

Overall, CDC found that the median rate of vaccination for measles, mumps, rubella, diphtheria, tetnus, and pertussis was approximately 95%. Specifically:

  • A median rate of 94.7% of kindergartners in the 2013-2014 school year received the MMR vaccine;
  • A median rate of 95% received the DTaP vaccine, which protects against diphtheria, tetanus and pertussis; and
  • A median rate of 93.3% received the varicella vaccination, which protects against chickenpox.

In some communities, opt out rates are soaring

However, the report also found that more parents are opting out of having their children vaccinated in certain communities, either on philosophical grounds or because of a belief that vaccines are dangerous to children.

How anti-vaxxers helped breathe new life into old diseases

Specifically, CDC found that:

  • MMR median vaccination rates among kindergarteners varied from 99.7% in Mississippi to 81.7% in Colorado, with a total of seven states and Washington, D.C., reporting rates lower than 90%;
  • DTaP median vaccination rates varied from at least 95% in 25 states to less than 90% in five states and Washington, D.C.; and
  • Varicella vaccination rates varied from at least 95% in nine states to less than 90% in eight states and Washington, D.C.

In addition, the report found that most states permitted parents to exempt children from vaccinations for religious reasons, while more than 12 states allowed parents to exempt children for "philosophical" reasons. Overall, CDC found that the median rate for nonmedical vaccination exemptions was 1.7%, varying from a high of 7% in Oregon and 6.1% in Vermont and Idaho, to a low of less than 0.1% in Mississippi.

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According to the report, the findings might overstate the unvaccinated population because some students obtain an exemption to enroll on time before belatedly receiving their vaccinations (Kaplan, "Science Now," LA Times, 10/16; Jenks, "Healthopolis," Roll Call, 10/17; Lawlor, Portland Press Herald, 10/17; CDC report, 10/17).

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