On December 2, 2021 the White House issued the following announcement: President Biden Announces New Actions to Protect Americans Against the Delta and Omicron Variants as We Battle COVID-19 this Winter. Of note in the release is the requirement to require international air travelers flying to the US to show to their airline a negative result based on a COVID-19 viral test taken within one day of departure, regardless of traveler nationality / citizenship or vaccination status. This changes previous guidance issued earlier in November that required a COVID-19 test taken in the three days before departure for vaccinated travelers, and one day for unvaccinated travelers.
In addition, masking will continue to be required for international and public travel through at least March 18, 2022. Failure to comply with masking requirements may lead to penalties and fines.
"If you plan to travel internationally, you will need to get a COVID-19 viral test (regardless of vaccination status or citizenship) no more than 1 day before you travel by air into the United States. You must show your negative result to the airline before you board your flight."