KEYWORDS:
Assessment, Valid Doses

BACKGROUND:
In June 2001, the ACIP approved the following recommendations regarding invalid vaccine doses: 1) allow a 4-day grace period to the minimum age and intervals for vaccination, and 2) invalid doses of vaccine should be repeated.

OBJECTIVE(S):
Determine the proportion of US children who received an invalid dose of vaccine and evaluate the impact on vaccination coverage levels if invalid doses were not counted.

METHOD(S):
We used provider validated vaccination histories of children 19-35 months of age from the 2000 NIS. Allowing for a 4-day grace period, any dose of vaccine administered before the ACIP recommended minimum age or before the minimum interval had elapsed was considered invalid. Change in vaccination coverage was determined by subtracting UTD coverage (based on number of doses received regardless of age or spacing) from the Valid-dose coverage (based on number of valid doses received).

RESULT(S):
Of 22,958 children, 10.5% had received at least one invalid dose of vaccine. Of the invalid doses, 51% were Hepatitis B, 19% DTP/DTaP, 12% were MCV, 15% were Varicella, and 4% were Polio. Most invalid DTP/DTaP doses (92%) were the fourth dose of the series; 96% of invalid polio doses were the first dose of the series; and 100% of invalid Hepatitis B doses were the third dose of the series. Excluding invalid doses resulted in a small changes in vaccination coverage; -2.2% for DTP/DTaP, -0.7% for polio, -6.5% for Hepatitis B, -1.4% for MCV, and -1.7% for Varicella.

CONCLUSIONS(S):
Approximately 595,000 children nationwide received at least one invalid dose of vaccine. The cost of revaccinating these children is substantial and may impact parents, physicians, and purchasers of the vaccine. Training of immunization providers regarding proper immunization timing should be conducted to reduce the administration of invalid doses of vaccines.

LEARNING OBJECTIVES:
Understand the frequency of invalid doses administered in the US.