The Centers for Disease Control and Prevention (CDC) is requiring air travelers arriving to the United States from the United Kingdom to test negative for the coronavirus within three days of their trip on the heels of the discovery of a more transmissible variant.

The order was signed Friday and went into effect Monday, December 28, 2020.

"President Trump is taking another step to protect the health of the American people by requiring air passengers arriving from the United Kingdom to test negative, via PCR or Antigen test, no more than 72 hours before departure from the U.K. to the United States," the CDC confirmed late last week.

"The public health authorities in the United Kingdom recently announced the discovery of a new variant of SARS-CoV-2. Viruses constantly change through mutation, and preliminary analysis in the U.K. suggests that this new variant may be up to 70 percent more transmissible than previously circulating variants."

While it acknowledges that "testing does not eliminate all risk" the CDC says that combining the new requirements with face masks, self-monitoring for symptoms and social distancing "can make travel safer" amid the pandemic.

Under the new order, travelers must provide written documentation of their lab test result either in hard copy or electronic form to their airline for confirmation before they can board. Airlines must deny boarding to passengers who choose not to get tested.

President Trump's March 14 Presidential Proclamation to suspend the entry of foreign nationals who visited the U.K. in the past 14 days reduced air travel to the U.S. from the U.K. by about 90 percent, the CDC noted. "This new order is consistent with the measures that have been taken so far to increase our ability to detect and contain COVID-19 proactively and aggressively."