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Children's Vaccines Health Center

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1 in 4 Toddlers Improperly Vaccinated

Timing of Immunization Is Crucial, and Many Children Get Shots Too Soon, CDC Says
WebMD Health News
Reviewed by Louise Chang, MD

April 29, 2008 -- Many young children in the United States have been under- or improperly vaccinated, and vaccine coverage rates are lower than previously reported as a result, the CDC says.

Using a modified method for calculating vaccine coverage, CDC researchers concluded that more than one in four babies and toddlers are out of compliance with government vaccination guidelines.

Instead of an 81% coverage rate among children aged 19-36 months, as has previously been reported, only about 72% of children in this age group have been adequately immunized, the CDC researchers conclude.

One problem is that many babies and young children who are vaccinated get their shots too early or too close together, CDC epidemiologist Elizabeth Luman, PhD, tells WebMD.

"If you get a vaccine too early or get doses too close together, they aren't as effective. They are not considered valid doses, and should be repeated," she says. "Our study found that this is happening quite often."

Childhood Vaccines: Timing Matters

The researchers analyzed the vaccination histories of about 17,500 children between the ages of 19 and 35 months whose parents took part in a 2005 nationwide immunization survey.

The aim was to determine if government vaccination recommendations were being followed.

Guidelines established by the Advisory Committee on Immunization Practices (ACIP) recommend which vaccines should be given and in what doses, at what age children should get the vaccines, the minimum age at which doses are considered valid, and the minimum time between doses within a vaccination series.

Previous vaccine coverage calculations have been based solely on the number of doses given, Luman tells WebMD.

When ACIP guidelines were considered, 19% of the children included in the survey were missing one or more doses of the recommended series of vaccinations and 6% had received at least one early, invalid vaccination.

Fourteen percent of the children missed the fourth dose of the diphtheria, tetanus, and pertussis vacine (DTaP); 9% had not been vaccinated against measles, mumps, and rubella (MMR), and 8% had not had a third dose of the polio vaccine.

About 14% of children had their third dose of the hepatitis B vaccination too early, and some toddlers received their first dose of measles vaccine while still protected by their mother's antibodies.

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