 Released by the United States Department of Health and Human Services (HHS) on February 1, 2007, the PSI was designed to resemble the Saffir-Simpson Hurricane Scale classification scheme.The index was replaced by the Pandemic Severity Assessment Framework in 2014, which uses quadrants based on transmissibility and clinical severity rather than a linear scale.The PSI was developed by the Centers for Disease Control and Prevention (CDC) as a new pandemic influenza planning tool for use by states, communities, businesses and schools, as part of a drive to provide more specific community-level prevention measures.