KEYWORDS:
vaccine shortages
BACKGROUND:
Between December 2000 and July 2002 vaccine shortages occurred for Td, DTaP, MMR, PCV7 and Varicella vaccines.
OBJECTIVE:
Evaluate the impact of vaccine shortages on immunization coverage levels from February 2000-November 2002 using data from immunization registries.
METHOD:
Four sentinel site immunization registries (3 states, 1 city) reported coverage rates during February-November 2002 for DTaP and PCV7 for cohorts of children at 7 months and 16 months of age. Trends in coverage rates for each age group by antigen and by sentinel site were analyzed using Change Point Analyzer 2.2. CUSUM charts and bootstrap analysis were used to detect if and when changes in the coverage trends occurred. Bootstrap methods were used to provide confidence levels for each estimated change point.
RESULT:
DTaP coverage levels for 16-month-old children decreased to levels one third to one half of baseline levels at three sites. The decrease in coverage began before March 2001 in these three sites and in two sites continued through November 2002. The third site showed a modest rebound beginning in September 2002. Among 7-month-old infants, three sites had a decrease in DTaP coverage of 6-8 percentage points after onset of the shortage; one site appears to be rebounding beginning in September 2002. PCV vaccination coverage levels at 16 months of age showed a rapid increase up until the first quarter of 2002. At that point coverage in two sites fell to one third of baseline and in the two other sites leveled off. A similar pattern was observed for PCV coverage for 7-month-old children.
CONCLUSION:
Immunization registries may be useful tools to measure the impact of vaccine shortages. Vaccine shortages had more impact in some sites than others. Of the sites that showed a decrease in coverage, only one site showed signs of rebounding as of November 2002. The impact of the DTaP shortage was greater on coverage at 16 months of age than at 7 months of age.
LEARNING OBJECTIVES:
Identify trends in vaccination coverage during vaccine shortages.
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