Interim Results: Influenza A (H1N1) 2009 Monovalent Vaccination Coverage --- United States, October--December 2009

Early Release

January 15, 2010 / 59(Early Release);1-5

In July 2009, the Advisory Committee on Immunization Practices (ACIP) issued recommendations for use of the influenza A (H1N1) 2009 monovalent vaccine (1). Recognizing that the vaccine supply would not be ample immediately but would grow over time, ACIP identified 1) initial target groups, consisting of approximately 160 million persons, and 2) a limited vaccine subset of the target groups, initially estimated at 42 million persons (and more recently estimated at 62 million persons), to receive first priority while the 2009 H1N1 vaccine supply was limited (1). ACIP recommended expanding vaccination to the rest of the population as vaccine supplies increased. To estimate 2009 H1N1 vaccination coverage to date for the 2009--10 influenza season, CDC analyzed results from the National 2009 H1N1 Flu Survey (NHFS) and the Behavioral Risk Factor Surveillance System (BRFSS) survey, conducted during December 27, 2009--January 2, 2010, and December 1--27, 2009, respectively. The results indicated that, as of January 2, an estimated 20.3% of the U.S. population (61 million persons) had been vaccinated, including 27.9% of persons in the initial target groups and 37.5% of those in the limited vaccine subset. An estimated 29.4% of U.S. children aged 6 months--18 years had been vaccinated. Now that an ample supply of 2009 H1N1 vaccine is available, efforts should continue to increase vaccination coverage among persons in the initial target groups and to offer vaccination to the rest of the U.S. population, including those aged ≥65 years (2).

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The findings in this report are subject to at least three limitations. First, the NHFS results presented in this analysis are based on data collected during a single week of interviews, and all results are based on self-report or parental report of 2009 H1N1 vaccination. Because of the limited size of the NHFS sample, confidence limits around estimates are large and final estimates might differ. Second, BRFSS and NHFS are subject to selection bias because of noninclusion of households with only cellular telephones (BRFSS) and households with no telephone service (BRFSS and NHFS). Finally, CASRO response rates and cooperation rates were low, particularly for NHFS.

Although influenza activity has declined in the United States in recent weeks, cases of 2009 H1N1 influenza, including cases of severe disease, continue to occur. The epidemiology of 2009 H1N1 influenza over the months ahead is unknown, but another rise in incidence, as occurred during the winter of the 1957--58 pandemic, remains possible (10). In addition, increases in influenza activity from seasonal influenza also might occur as the season progresses. Vaccination remains the best way to prevent influenza infection and influenza-related hospitalizations and deaths.

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