Starting Monday in the UK, passengers must have a negative Covid-19 test within three days of boarding a flight to the US.
“Today, President Trump is taking another step to protect the health of the American people,” the statement said.
But according to researchers on the Centers for Disease Control and Prevention’s Covid-19 Response Team, testing three days before the flight may not achieve much – reducing the risk of the virus spreading by only 5-9%.
Covid-19 tests often miss recent infections, so a person can test negative and already be infected because it does not release enough viruses to detect it.
“Many people will miss the test 72 hours before the flight,” said Dr. Peter Hotez, an infectious disease specialist at Baylor College of Medicine, indicating that the new variant appeared in the UK three months ago and is likely already in the US.
Health officials have been keen to limit the spread of the variant in the UK, which appears to be transmitted more easily than other strains of the Coronavirus.
The CDC did not respond to requests for comment for this story.