Over-Immunization Among Children

Little is known about the extent of extraimmunization (over immunization), i.e., vaccine doses given in excess of the recommended schedule, and whether it should be a concern. The objective of this study was to determine the extent and cost of extraimmunization in children and to identify associated factors.

The data are from the United States National Immunization Survey (1997) in which telephone interviews were conducted with parents of 32,742 19-to-35-month-old children and vaccination histories were collected from health care providers for 22,806 of these children (overall response rate, 68.5%).

Frequency of extraimmunization was less than 5% for each vaccine considered except poliovirus (14.1%). Overall, 21% of children were extraimmunized for at least one vaccine vs 31% underimmunized for at least one vaccine. The strongest contributors to extraimmunization were having more than one immunization provider. Children seen only in public health clinics were significantly less likely to be extraimmunized. Annual costs associated with extraimmunization for these children were estimated conservatively at $26.5 million.

Comment: The cost overrun is staggering for this group of pre-schoolers. Possible adverse health effects of overimmunization are not addressed in this article, one being the excessive exposure of adults to polio virus in the case of Sabin oral vaccine. Statewide computer networks could go a long way toward sharpening the record keeping. Underimmunization remains the greater issue in pre-school children. - R. A.