Extraimmunization among US children

Little is known about the extent of extraimmunization, ie, vaccine doses given in excess of the recommended schedule, and whether it should be a public health concern.

To determine the extent and cost of extraimmunization in children and to identify its associated factors.

United States 1997 National Immunization Survey, in which telephone interviews were conducted with parents of 32742 19- to 35-month-old children and vaccination histories were collected from health care providers for 22806 of these children (overall response rate, 68.5%). Estimates were weighted to represent the full sample.

Frequency of extraimmunization compared by vaccine type as well as with adequate immunization; factors associated with extraimmunization; and vaccine and visit costs associated with extraimmunization.

Frequency of extraimmunization was less than 5% for each vaccine considered except poliovirus (14.1%). Overall, 21% of children were extraimmunized for at least 1 vaccine vs 31% underimmunized for at least 1 vaccine. In a multivariate model, the strongest contributors to extraimmunization were having more than 1 immunization provider (odds ratio [OR], 2.8; 95% confidence interval [CI], 2.4-3.2) and having multiple types of providers (eg, private and public health department; OR, 2.0; 95% CI, 1.6-2.4). Children seen only in public health department clinics were significantly less likely to be extraimmunized (OR, 0.3; 95% CI, 0.2-0.3). Annual costs associated with extraimmunization for this cohort of children were estimated conservatively at $26.5 million.

These data indicate that extraimmunization can be costly. The challenge is to reduce extraimmunization without interfering with more important efforts to combat underimmunization. Improvements in immunization record keeping and sharing practices may help reduce extraimmunization.