Influenza A (H1N1) 2009 Monovalent Vaccination Among Adults 25-64 Years with Asthma--United States, 2010

Background:  The 2009 pandemic influenza A (H1N1) virus quickly spread around the world from the initial April outbreak in Mexico and United States. Adults 25-64 years with medical conditions associated with influenza-related complications were among the priority groups recommended for 2009 H1N1 vaccination. People currently with asthma comprise about 40% of this group.

Objectives: To examine the 2009-10 national and state-specific 2009 H1N1 vaccination coverage among US adults 25-64 years with asthma.

Methods: Data from the Behavioral Risk Factor Surveillance System (BRFSS) March through June 2010 interviews using the influenza supplemental survey were analyzed to estimate national 2009 H1N1 vaccination received October 2009 through February 2010. Multivariable logistic regressions were performed to identify factors independently associated with vaccination at the national level.  To obtain state-level coverage, we analyzed November 2009-June 2010 interviews and used survival analysis to estimate coverage through May 2010.

Results:  Among U.S. adults 25-64 years with asthma, 25.5% (95% confidence interval: 23.9-27.2) received the 2009 H1N1 vaccination; those 25-49 years had lower coverage at 22.9% (20.7-25.2) compared to adults 50-64 years, 30.2% (28.0-32.5). Characteristics independently associated with higher vaccination levels in the group of 25-64 were having a primary doctor, having other high-risk conditions, and receiving seasonal influenza vaccination. 

Conclusions:  National 2009 H1N1 vaccination coverage among adults 25-64 years with asthma was more than 10 percentage points lower than seasonal coverage in this group (coverage of either vaccine did not reach the Healthy People 2010 objective of 60% for 18-64 high risk persons) and varied widely by state and demographic characteristics. Further coverage studies will compare different high-risk groups, priority groups, and states to identify best practices. Findings from these studies will help improve national and state-specific pandemic influenza response plans to improve vaccination of at risk groups.