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Since 1996, the number of immunization injections per doctor visit has more than doubled. According to a new study by Children's Hospital of NewYork-Presbyterian/Columbia University Medical Center, as the number of injections has risen so have the number of parents and providers that postpone opportunities to get necessary vaccines a phenomenon they characterize as the pin cushion effect.

The number of immunization injections increased from an average of 1.3 per visit in 1996 to 3.2 per visit in 2000. During this period, as the number of injections per visit increased, the number of missed opportunities rose from 28 percent to 34 percent, and the highest rate of missed opportunities was associated with the maximum number of injections needed at that visit. The findings will be presented today at the Pediatric Academic Societies meeting in San Francisco.

Both providers and parents have concerns about an excess of injections per visit. As a result of these concerns, they postpone or skip vaccines leading to intentional missed opportunities, says Dr. Matilde Irigoyen, director of the division of general pediatrics and professor of clinical pediatrics and clinical public health at Columbia University College of Physicians Surgeons and attending pediatrician at Children's Hospital of NewYork-Presbyterian.

Dr. Irigoyen continues: As in other studies, providers appear to prioritize vaccines based on the perceived risk to child. One positive is that there appears to be a desensitization process, with providers and parents becoming used to an increasing number injections per visit, and what was 'too much' becomes accepted when new injections are introduced. Also, increased availability of combination vaccines should reduce the number of intentional missed opportunities. However, our analyses suggest that whatever the current maximum injections is, that maximum will have a substantially higher probability of missed opportunities.

Since 1998, when children needed a maximum of five injections at a visit, 90 percent of the five-injection visits had missed opportunities. 1996-97, when the maximum number of injections was only four per visit, the missed opportunity rate for four-injection visits was also over 90 percent. As soon as the fifth injection was added in 1998, the missed opportunity rate for the four-injection visit dropped to 44 percent, a rate that further declined to only 27 percent in 2000. A similar pattern was found in 1996-1997 when the fourth immunization was added and the missed opportunity rate for three-injection visits dropped from 95 percent to only 45 percent.

The study was conducted in a pediatric practice network in the low-income community of Northern Manhattan with 22,515 participating children.