The US Centers for Disease Control and Prevention is now expanding surveillance across four major international airports to screen for the Omicron variant of the coronavirus, the agency’s director, Dr. Rochelle Walensky, recently announced.

Dr. Walensky said the CDC will screen travelers through the testing service XpresCheck at Hartsfield-Jackson Atlanta International Airport, John F. Kennedy International Airport, Newark Liberty International Airport, and San Francisco International Airport. According to Walensky, these four airports are the busiest.

All this comes as the world is on high alert after the Omicron variant was detected in several southern African countries. It sparked countries worldwide to impose new travel restrictions on travelers.

The Biden administration has placed travel restrictions on eight southern African countries, including South Africa since South African health authorities alerted the world about the new variant, CNN reports.

Dutch health officials, however, said they found the new Omicron variant of the coronavirus nearly two weeks before South African health officials reported it, indicating that it was spreading in Western Europe before the cases were identified in South Africa

Belgian and German officials have also confirmed the variant was in their countries before South African health officials alerted the world on Nov. 24 of its existence.

Despite the discovery and travel restrictions, Delta Air Lines says it plans to continue flights from Atlanta to Johannesburg. United Airlines has no plans to reduce service between Newark and Johannesburg and plans to restart its route to Cape Town, South Africa this December.

The CDC says it’s keeping in close touch with both state and local health officials to monitor the situation.

“CDC is evaluating how to make international travel as safe as possible,” said Walensky. “We are holding regular, even daily calls, with local county and state health officials and our public health partners. These calls include state, county, and city health officials, state epidemiologists, laboratory directors, and partners from public health organizations.”

She added, “we are continuously working closely with our public health partners, both here in America and around the world.”