Starting Monday in the UK, passengers must have a negative Covid-19 test within three days of boarding a flight to the United States.
“Today, President Trump is taking another step to protect the health of the American people,” according to the statement.
But according to researchers on the CDC’s Covid-19 response team, testing three days before a flight might not accomplish very much — reducing the risk of spreading the virus by just 5 to 9%.
A federal official told CNN that the new order is just one layer in a multi-layered approach to curtail the spread of the new variant, which appears to transmit more easily than other coronavirus strains.
In March, the CDC cut off travel from the UK for foreign nationals, which brought travel from the UK to the US down 90%, from about 30,000 to 3,000 passengers a day, the official said.
In addition, the CDC has recommendations for international travelers, including getting tested one to three days before a flight and three to five days after travel, combined with staying home for seven days after travel, even if they test negative.
Covid-19 tests often miss recent infections, so someone can test negative and actually be infected because they’re not shedding enough virus to be detected.
“Testing 72 hours before a flight is going to miss a lot of people,” said Dr. Peter Hotez, an infectious disease specialist at the Baylor College of Medicine, who pointed out that the new variant appeared in the UK three months ago and is likely already in the United States.