Under a new policy from the Centers for Disease Control and Prevention, all were required to produce a negative COVID-19 test before boarding their flights to the United States. But that’s an imperfect means of protection, shown to miss anywhere from 30% to 70% of people who are in the early stages of an infection.

The sudden return of Chinese visitors may inadvertently throw a bit of fuel onto the dumpster fire of COVID-19 cases that continues to burn in the United States. But the CDC is also concerned about a more remote — and far scarier — possibility: that a traveler from China infected with a new coronavirus variant could enter the country and jump-start a fresh wave of transmission and illness.

“New variants can arise anywhere there’s uncontrolled infection, and COVID is spreading through China like wildfire,” said Harvard University infectious disease specialist Dr. Jonathan Li.

The Omicron variant seems to have triumphed over all other versions of the SARS-CoV-2 virus, Li noted. But patients with weakened immune systems remain the most likely incubators of new variants, “and I have no doubt the absolute number of immunosuppressed patients in China is extensive,” he said.

As for whether those circumstances spawn new versions of the pandemic virus and how far they might travel, “we’ll have to see,” Li added.

That’s the mission of the Traveler Genomic Surveillance program, a virus-hunting initiative the CDC quietly stood up in September 2021. Its foot soldiers were deployed at LAX for the first time on Tuesday morning.

With smiles evident behind face masks and thank-you gifts in hand, these sentinels in plain black scrubs are tasked with seeking volunteers whose flights originated in China who are willing to swab their noses to support the search for new viral variants. Those who agree will receive a free take-home COVID-19 test as a token of America’s appreciation.

While new to LAX, the CDC program already operates in international airports in San Francisco, Seattle, New York City, Newark, N.J., Washington, D.C., and Atlanta. Over the past 15 months, it has persuaded about 80,000 travelers from every corner of the world to participate.

Health officials hope the new testing site at LAX will help them identify new coronavirus variants that may be brewing in China.

(Gary Coronado/Los Angeles Times)

Providing U.S. health officials with an early warning of new variants is one aim of the CDC’s public-private partnership with Ginkgo Bioworks, a medical testing company, and XpresCheck, which grew out of a spa-services company offering massages, mani-pedis and wellness products in a dozen U.S. airports.

The other key aim is to fill in the absent or incomplete pictures of SARS-CoV-2 variants circulating in countries where genetic sequencing is either not being conducted or not being shared with the international community.

China is one of those international blind spots. As the pandemic has progressed and the government carried out billions of coronavirus tests as part of its “zero COVID” policy, its scientists have shared only a handful of genetic sequences with their counterparts overseas.

“There’s been very little data from China” uploaded to internationally available sites, said Dr. Cindy Friedman, chief of the CDC’s Travelers’ Health Branch. “That’s why travelers as sentinels are so valuable.”

A central feature of the program is what it does not do: follow or track volunteers who, despite testing requirements, might arrive in the United States infected.

Even in the unlikely event that an international traveler is found to carry a new genetic variant, the CDC would be unable to use that volunteer’s sample to track him or her down.

“This is by no means a border-control program designed to find and isolate” individuals, Friedman said. “This is a surveillance program” aimed at providing early warning of an impending threat.

That is one of the reasons the program is not carried out by CDC employees, who maintain a presence at international airports to man “quarantine stations.” Instead, employees of XpresCheck await the arrival of specific flights and approach potential volunteers outside of immigration and customs areas.

Until recently, they’ve been dressed in orange scrubs and led willing travelers to bright orange booths bearing logos of the CDC, XpresCheck and Ginkgo Bioworks. The switch to black scrubs is new with the expansion to LAX.

“We don’t want people to think this is a mandatory program,” said Ezra Ernst, president and CEO of ExpresTest Inc., which, with XpresSpa and XpresCheck, operates under the corporate banner of Xwell. “’Would you help?’ is a phrase we use often.”

Claire Altieri (seated) works with colleagues Ryan Kramer and Amy Schierhorn to set up the new coronavirus testing site at LAX’s Tom Bradley International Terminal. Workers began asking volunteers to provide samples on Tuesday.

(Gary Coronado/Los Angeles Times)

Once a willing traveler swabs her nose and answers some questions about her starting point and route to the United States, her specimen is mixed with four others to create a “pooled sample” for less expensive and more efficient testing by Ginkgo Bioworks labs across the country. If a pooled sample comes up positive, workers can genetically sequence each of the specimens that were grouped together to identify the one with unusual genetic characteristics.

If the surveillance program detects a new coronavirus variant, “we can buy science weeks and months of knowing what’s coming,” Friedman said. “That buys time to understand the variant, and what adjustments need to be made,” she added.

During the initial weeks of the Omicron surge, the program was the first to pick up on two subvariants that came to be known as BA.2 and BA.3. The CDC reported them to the global database maintained by the GISAID Initiative, allowing scientists to quickly assess whether and how their novel mutations affected their transmissibility, their ability to sicken, and their ability to overcome vaccine protection.

The program’s next move may take it from airport arrivals terminals to the aircraft lavatories. Friedman said the CDC hopes to convince commercial airlines to allow the collection of wastewater from toilets on long-distance international flights so it can be used for sampling and genetic sequencing.

“On a long-haul flight, everybody uses the bathroom,” Friedman said. Even if travelers decline to volunteer at airports, wastewater surveillance from aircraft “will give you a picture” of what passengers may carry into the United States, she said.

Researchers in Australia partnered with Qantas Airways to assess the feasibility of aircraft wastewater testing and concluded it could be an “effective tool” for “monitoring the importation of SARS CoV-2 and other clinically significant pathogens.”

Rolling it out on a large scare poses legal, ethical and technical challenges for airlines, which have not yet signed on. But “that’s the vision going forward,” said Friedman, who expressed optimism that commercial carriers “would be great partners.”