[Correction to original post]
On December 2, the U.S. Centers for Disease Control and Prevention (CDC) revised the current Global Testing Order, requiring all air travelers, regardless of citizenship or vaccination status, to test for COVID within one day* of departure to the U.S. beginning Monday, Dec 6, 2021.
For more information please see the links below:
CDC Tightens Testing Requirement for International Travel to the US to One Day: Press Release: https://www.cdc.gov/media/releases/2021/p1203-covid-testing-tightens-intl.html
*Original post showing “24 hours” changed to “one day.” According to the CDC FAQ under “Timing Requirements”:
The 1-day period is 1 day before the flight’s departure. The Order uses a 1-day time frame instead of 24 hours to provide more flexibility to the air passenger and aircraft operator. By using a 1-day window, test acceptability does not depend on the time of the flight or the time of day that the test sample was taken.
For example, if your flight is at 1pm on a Friday, you could board with a negative test that was taken any time on the prior Thursday.