Comparison of H1N1 and seasonal influenza vaccine usage rates in Massachusetts, December 2009

Vaccination strategies targeting age-specific high-risk groups have been prioritized to mitigate and respond to the recent H1N1 epidemic. However, there were marked differences in vaccine availability in Massachusetts. By 11/30/2009, half as much H1N1 vaccine was available (1.4 million doses) compared to seasonal influenza vaccine (2.75 million). In addition, H1N1 vaccine was available six weeks later than seasonal influenza vaccine: 10/2/2009 marks H1N1 availability versus 8/13/2009 for seasonal. The Behavioral Risk Factor Surveillance System (BRFSS) and the National 2009 H1N1 Flu Survey (NHFS) are state-based, random-digit-dialed telephone surveys that collect immunization history information. Methods We calculated descriptive statistics and compared rates of vaccine usage in Massachusetts for December 2009. We used BRFSS data to analyze adult rates and NHFS data for pediatric rates. Results Cumulative H1N1 vaccination rates for those <18 years was 39% (n=237, 95% CI 30-48%) versus 56% (n=233, 95% CI 46-66%) for seasonal flu; high-risk 18-49 year-olds was 26% (n=65, 95% CI 13-47%) versus 39% (n=66, 95% CI 24-57%). For those aged >65 years, cumulative H1N1 vaccination rates were 5% (n=230, 95% CI 3-10%) versus 73% (n=232, 95% CI 64-80%) for seasonal influenza. Statistical differences between vaccine types within age-specific groups were p<0.001, p=0.1085, and p<0.001, respectively. Conclusion These results pre-date widespread availability of H1N1 vaccine, but correspond to a period of widespread availability for seasonal influenza vaccine. As a result of increased vaccination time and availability, rates for seasonal influenza vaccination are dramatically higher than H1N1 vaccination in all age groups in this mid-season assessment.