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Children's Vaccines Health Center

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Child Vaccines: Some Parents Ill at Ease

Does the private right of parents to not vaccinate their kids trump the greater public good?

Herd Immunity

Penelope H. Denehy, MD, professor of pediatrics at the Warren Alpert Medical School of Brown University in Providence, R.I., notes that in addition to protecting individual children against infectious diseases, universal vaccinations cover those children who for medical reasons cannot be vaccinated, a concept known as "herd immunity."

"One of the things we know quite clearly is that if there are enough parents in an area who [refuse to vaccinate], there actually then becomes a large-enough group of non-immune kids to actually sustain outbreaks," she tells WebMD. "There's an area in Colorado where the rates of pertussis [whooping cough] were quite high because there was enough of a population who were not immunized to sustain the passage of pertussis around the community."

In addition, even if an unvaccinated child is protected by herd immunity at home, if that child travels with her family, she runs a high risk of infection from a person from a part of the world with low vaccination rates, as happened in the case of the Indiana measles outbreak.

Vaccination for children entering school is mandatory in all 50 states, but all states allow exemptions for medical reasons.

"Even in a well-vaccinated population, there are going to be some children who can't be vaccinated, either because they're too young -- for measles less than 12 months of age -- or they may have cancer chemotherapy or some other compromising medical condition that makes it not possible to vaccinate them," says Lance Rodewald, MD, director of the immunization services division at the CDC's National Center for Immunization and Respiratory Diseases.

Rodewald notes that there is also a low but still significant failure rate for some vaccinations: "For example, with one dose of measles vaccine there's a 4% to 5% failure rate, and with two doses of course it's much smaller, but still there will be some susceptibles in the population," he tells WebMD.

In addition to allowing medical exemptions for immunization, all states except Mississippi and West Virginia also allow exemptions from immunizations for deeply held religious beliefs, and 18 allow exemptions for "philosophical" objections, according to the NVIC.

In states where this is allowed, 2.54% of parents declined vaccines, according to a Johns Hopkins researcher.

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