Starting from Monday in the UK, passengers must undergo a negative Covid-19 test within three days of boarding and flying to the United States.
The statement said: “Today, President Trump is taking further measures to protect the health of the American people.”
But according to researchers from the CDC Covid-19 Response Team, tests conducted three days before the flight may not work well-reducing the risk of virus transmission by 5% to 9%.
Covid-19 tests usually miss the most recent infection, so someone can test negative and actually get infected because they did not release enough virus to be detected.
Dr. Peter Hotez, an infectious disease expert at Baylor College of Medicine, said: “The test 72 hours before the flight will be missed by many.” It may already be in the United States.
Health officials have been eager to limit the spread of the British variant, which seems to spread more easily than other coronavirus strains.
The CDC did not respond to a request for comment on this matter.