On April 26, 2009, public health officials declared a national public health emergency after the discovery of a new Influenza A (H1N1) strain was first identified in Mexico and then in the U.S. A new pandemic H1N1 swine flu vaccine was quickly licensed and made available to the public in October of 2009, but a 2011 study of the effectiveness of the 2009 pandemic H1N1 swine flu vaccine found it had an overall effectiveness of only 56 percent.
