Monitoring county-level vaccination coverage during the 2004-2005 influenza season

BACKGROUND: During the 2004-2005 influenza season, the United States faced a sudden shortage of influenza vaccine. In response, the Centers for Disease Control and Prevention (CDC) and the Advisory Committee on Immunization Practices (ACIP) recommended prioritizing vaccination for persons aged 65 and older and others at high risk. To monitor subsequent vaccination coverage, several questions about influenza vaccination were added to the ongoing Behavioral Risk Factor Surveillance System (BRFSS). This study provided real-time county-level estimates of influenza vaccination coverage from the BRFSS each month from October 2004 through January 2005. METHOD: The methods used a variation of small area estimation procedures suitable for situations in which most small areas have few or no survey respondents, and rapid assessment is essential. Both model-based methods and nonparametric spatial-smoothing methods were used in a three-step procedure. RESULTS: The highest vaccination rates during the 2004-2005 influenza season were seen in the upper Midwest and the Southeast. Areas with the lowest vaccination rates were the intermountain West, southern California, portions of Washington and Oregon, and various areas across the Eastern United States, often coinciding with urban areas. Intrastate variations were especially pronounced in the Eastern United States, particularly in Georgia, Florida, Tennessee, Kentucky, North Carolina, Virginia, and New York. These states all had areas with low immunization rates as well as areas with high rates. CONCLUSIONS: The results showed that vaccination coverage varied significantly across states and substate regions. Our findings show that this methodology can provide estimates with reasonable reliability for planning during public health emergencies.