The CDC said it is working to modify the current global testing order for travel as more data comes in on the Omicron variant, and recommends all passengers should still get a viral test 3-5 days following travel. Unvaccinated travelers should quarantine upon arrival, the CDC said.

Speaking with CNN’s Erin Burnett late Tuesday, U.S. Surgeon General Vivek Murthy said travel restrictions won’t “permanently keep out a variant.” But he said they can help buy time to “vaccinate more people, learn more about the variant [and] work on strengthening even further travel safety measures, including testing.”

“The CDC is considering a number of measures — right now, it hasn’t fully decided on what it’s implementing,” Murthy continued. “But I do believe some of the measures it’s considering will have a substantial impact on our ability to detect the virus before it arrives here.”

Earlier this month, the administration and the CDC stipulated that those traveling to the U.S. must show proof of vaccination as well as proof of a negative Covid-19 test taken three days prior to boarding an airplane, replacing quarantine measures that had previously been in place. Unvaccinated Americans who wish to return to the U.S. have been subject to stricter testing requirements, testing one day before their departure and again post-arrival.

Earlier Tuesday, White House Coronavirus Response Coordinator Jeffrey Zients told reporters various health agencies are together evaluating data on the Omicron variant, particularly its transmissibility and severity, as well as how much protection current vaccines convey against it, before making any moves to change travel requirements.

The Biden administration has already banned travel from South Africa, which first reported the new variant, as well as from nearby Botswana, Namibia, Zimbabwe, Lesotho, Eswatini, Malawi and Mozambique. But there have been indications that the variant may have circulated in Europe first, raising questions about whether the U.S. might again shut down flights from Europe, mere weeks after they had been lifted.

A U.S. airline industry official previously told POLITICO that carriers have had the means to collect passenger information, including vaccine status, in place since January for pre-departure testing. The CDC doesn’t necessarily use that information — legal name, date of birth, email address, phone number, destination of travel and proof of vaccination that can be linked back to a government or public health agency as required by the Nov. 8 reopening — unless it has to, the industry official said.

Some experts say these new steps are coming far too late.

“It appears to me, almost two years into a global crisis, that the US CDC is only now making a few calls to consider options to protect American travelers,” Rick Bright, CEO of the Rockefeller Foundation’s Pandemic Prevention Institute and former director of the Biomedical Advanced Research and Development Authority, told POLITICO, calling the administration’s pace “disappointing.”

“It’s likely to result in yet another poorly planned and executed knee jerk reaction. Do they have the rapid testing infrastructure in place? Will travelers be able to comply with the mandatory policy free of cost or will they need to pay $25 to $50 per test and use a complicated service that international travelers now endure?” he said in a statement. “It’s [way past] time to get serious about ending this pandemic.”

David Lim contributed to this report.