Suspension of Entry as Immigrants and Nonimmigrants of Certain Additional Persons Who Pose a Risk of Transmitting 2019 Novel Coronavirus: Proclamation 9993 by the President of the United States of America, March 11, 2020 [open pdf - 254KB]
Proclamation 9993 issued by the president on March 11, 2020 states: "The Centers for Disease Control and Prevention (CDC), a component of the Department of Health and Human Services, has determined that the virus [COVID-19] presents a serious public health threat, and CDC continues to take steps to prevent its spread. But CDC, along with State and local health departments, has limited resources, and the public health system could be overwhelmed if sustained human-to-human transmission of the virus occurred in the United States on a large scale. Sustained human-to-human transmission has the potential to cause cascading public health, economic, national security, and societal consequences."
Federal Register: http://www.gpo.gov/fdsys/browse/collection.action?collectionCode=FR
Federal Register (March 16, 2020), v.85 no.51, p.15045-15048