(CNN)Passengers arriving in the United States from the United Kingdom must test negative for Covid-19 before departure, the US Centers for Disease Control and Prevention announced late Thursday.
Passengers will be required to have a negative PCR or antigen test within 72 hours of boarding their flight from the UK to the US. 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%. 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 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 US 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.
Fauci says estimate for herd immunity may be higher
More than a million people in the US have received the first dose of a Covid-19 vaccine just in the past 10 days. But hundreds of millions more will need to be vaccinated to reach herd immunity and ultimately stop the virus' spread.
Dr. Anthony Fauci estimated that 70-85% of the population needs to get vaccinated against the novel coronavirus in order to achieve herd immunity, which is when a large enough portion of the community is immune to the virus that its spread is unlikely.
"This is purely an estimate," Fauci said. "I don't want anyone to go bonkers over this. These are all estimates."
The top end of that estimate is higher than Fauci's previous estimate that 70-75% of the population would need to be vaccinated.
Several factors go into estimating what percentage of the population needs to be vaccinated to achieve herd immunity, including the rate of spread of the virus and the effectiveness of the vaccine.
Fauci, director of the National Institute of Allergy and Infectious Diseases, said his estimate "evolved for no great reason." He said he made his latest estimate after considering that about a 90% vaccination rate is needed to control the spread of measles.
"I'm extrapolating from measles, which has a vaccine that's 98% effective," Fauci said. "But (measles is) such an amazingly transmissible disease -- even more transmissible" than the novel coronavirus.
The Moderna and Pfizer vaccines are about 95% effective against the coronavirus.
BioNTech CEO Ugur Sahin similarly raised his vaccination estimates this week. On Tuesday, he said the UK variant of the coronavirus may require countries to vaccinate higher shares of population, raising the bar for achieving herd immunity.
"(On) the topic of heard immunity there is always the discussion about 60-70 percent," Sahin said. "But if the virus becomes more efficient in infecting people, we might need even a high vaccination rate to ensure that normal life can continue without interruption."
"But 60-70 percent of vaccination rate will really dramatically change the situation," Sahin added. "It is not that we have to deal with outbreaks if the virus becomes more effective, but it still would provide a more or less normal life."
