Despite interim recommendations that the Hib – Haemophilus influenzae type b – vaccination be deferred only among children who were not at high risk for disease, and that the primary series normally given during the first year of life be provided as usual during the 2008-2009 Hib vaccine shortage, data indicate that vaccination coverage for the primary series was significantly decreased at numerous sites across the United States during that period.
Data from eight Immunization Information System (IIS) sentinel sites across the United States, which included nearly 123,000 children, showed that compared with coverage of two other vaccines given at similar ages – the PCV7 (7-valent pneumococcal conjugate) vaccine and the DTaP (diphtheria, tetanus, and acellular pertussis) vaccine – completion of the primary Hib series by 9 months of age was 7.8-10.3 percentage points lower in seven of the eight sentinel sites during the shortage period, Karen E. White of the Minnesota Department of Health, St. Paul, and her colleagues reported in the March issue of Pediatrics.
Specifically, the percentage point differences in coverage between the Hib and PCV7/DTaP vaccines were –8.6, –7.8, –9.7, –9.1, –10.1, –9.5, and –10.3 at the sentinel sites in Colorado, Michigan, Minnesota, New York City, North Dakota, Oregon, and Wisconsin, respectively, the investigators found (Pediatrics 2011;127:e707-12).
Only the Arizona sentinel site had no significant difference in the vaccination rates, they said.
A comparison of the coverage data during the 2008-2009 shortage vs. coverage data from the prior year (2006-2207) in each of the seven sentinel sites that had lower Hib coverage in 2008-2009 showed that Hib coverage previously was better than, or similar to, coverage for PCV7/DTaP in five of the seven sites, with percentage point differences ranging from +1.3 to +6.1. In the remaining two sites (Oregon and Wisconsin), Hib coverage previously was less than coverage for the other vaccines, but the magnitude of the difference was less during 2006-2007 than what was observed during the shortage (–3.5 vs. –9.5 and –1.7 vs. –10.3 percentage points, respectively).
This study was undertaken after public health officials in Minnesota observed low Hib vaccination coverage of the primary series there during the shortage. The findings, although not generalizable to the entire United States, do suggest that the reduced coverage was not isolated to Minnesota.
Possible explanations for the reduced coverage include limited availability of vaccine to specific provider practices at certain times, challenges in incorporating the combination vaccine product into provider practices, and differences in the availability of Hib vaccine between private and public vaccine stocks, Ms. White and her associates said.
Also, despite widespread efforts by the public health community to disseminate information about the interim recommendations through a variety of publications and media outlets, a "significant minority" of clinicians considered the recommendations to be unclear, they noted.
The findings from the IIS – a collaborative project between the Centers for Disease Control and Prevention and several city- and state-based information systems that is designed to evaluate immunization programs and estimate vaccine coverage – underscore the importance of the processes of sharing clear recommendations during vaccine shortages and providing public health support to vaccine providers to carry out the recommendations, they concluded.
Ms. White and her associates stated that they had no relevant financial disclosures.