(Bloomberg) -- The Centers for Disease Control and Prevention is considering tightened travel recommendations and rules as health officials try to slow the Covid-19 omicron variant’s entry to the U.S.

The agency is looking measures such as narrowing the testing window for travelers into the country and adding quarantine requirements in certain cases, CDC Director Rochelle Walensky said Tuesday on a call with reporters. It’s also expanding surveillance programs at four major airports to test for Covid from specific international arrivals.

“As we have done throughout the pandemic, CDC is evaluating how to make international travel as safe as possible,” she said on the call. 

The country last week imposed travel restrictions that bar arrivals from foreign nationals who ave been in any of eight southern African nations in the past 14 days. The administration hasn’t said how long those measures will be in place.

“Based on the data and the science, the medical team will make a recommendation on any changes to international travel policy,” said Jeff Zients, President Joe Biden’s Covid-19 response coordinator. 

Walensky said there remains “no evidence of omicron in the United States,” though Biden said Monday it’s “almost inevitable” the variant will arrive. 

“I do believe with all of our international travel policies that have helped to keep Americans safe as well as for our really robust surveillance system” for identifying variants genetically, Walensky said, “we do have detection mechanisms that we need in place in order to find it, should and when it occurs.”

©2021 Bloomberg L.P.