The San Francisco International Airport is among the four major international airports with now expanded surveillance under the U.S. Centers for Disease Control and Prevention over the threat of the Omicron variant of the coronavirus.

In a White House COVID-19 press briefing, Dr. Rochelle Walensky said that the CDC is intensifying its monitoring with a testing service, XpresCheck, at airports. Other airports that will implement the surveillance are the Hartsfield-Jackson Atlanta International Airport, John F. Kennedy International Airport and Newark Liberty International Airport, KPIX reported.

Walensky said the four major airports are considered the busiest nationwide.

Late last week, new travel restrictions were announced by the Biden administration to impose ban from eight southern African countries, with South Africa – where the new variant was first detected – included.

Atlanta-headquartered Delta Air Lines, however, intends to retain its Atlanta-Johannesburg flights.

The same plan is also expressed by United Airlines, saying that it will not reduce its service between Johannesburg and Newark. It also said it will pursue its plan to restart its flights to Cape Town, South Africa.

XpresCheck’s parent company XpresSpa said it extended its biosurveillance undertaking with the expansion. Launched in September, the program gave testing for travelers from India coming into JFK, Newark and San Francisco.

“CDC is evaluating how to make international travel as safe as possible,” Walensky said, saying that it included “critical partner testing closer to the time of flights and considerations around additional post-arrival testing and self-quarantine.”

“This program allows for increased Covid testing for specific international arrivals,” Walensky furthered, “increasing our capacity to identify those with Covid-19 on arrival to the United States and enhancing our surveillance for the Omicron variant.”

Furthermore, she assured that the CDC and the airlines are working together “to collect passenger information that can be used by CDC and local public health jurisdictions to enhance contact tracing and post-arrival follow-up should a case be identified in a traveler.”