The 2009 pandemic influenza A (H1N1) virus (2009 H1N1) was first identified in April 2009 and quickly spread around the world. The first doses of influenza A (H1N1) 2009 monovalent vaccine (2009 H1N1 vaccine) became available in the U.S. in early October 2009. Because people with asthma are at increased risk of complications from influenza, people with asthma were included among the initial prioritized groups.