WASHINGTON (CNN) — Passengers arriving in the United States from the United Kingdom must test negative for COVID-19 before departure, the U.S. Centers for Disease Control and Prevention announced late Thursday night.

Passengers will be required to have a negative PCR or antigen test within 72 hours of boarding their flight from the UK to the U.S. Passengers are also required to provide documentation of their laboratory results, either as a hard copy or electronic.

Airlines are required to confirm the test results before the flight and passengers will not be permitted to board if they refuse a test or do not provide documentation.

The order is in response to a new coronavirus variant that is said to have originated in the UK and is potentially more transmissible. Since the discovery of the variant, more than 40 countries have restricted travel from the UK and in some cases, also travel from other countries that have documented cases with the variant.

“On March 14, President Trump issued a Presidential Proclamation to suspend the entry of foreign nationals who visited the United Kingdom in the past 14 days,” the CDC said in a statement. “This has reduced air travel to the U.S. from the U.K. by about 90 percent. This additional testing requirement will fortify our protection of the American public to improve their health and safety and ensure responsible international travel.”

The agency said the order will be signed Friday and will go into effect on Monday.

Genetics experts have expressed preliminary concerns that the COVID-19 vaccines might have less efficacy against this new variant. Pfizer and Moderna are testing their vaccines to see if they work against the new variant.

The UK coronavirus variant has not been identified through genetic sequencing efforts in the US, the CDC said Tuesday. But that may be because the U.S. surveillance system isn’t catching it.

“It could be in the United States and we might not have yet detected it,” Assistant Secretary for Health Admiral Brett Giroir said Monday.

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