Public-health officials continue to track new COVID-19 variants even though the pandemic was declared officially over last month. Experts from the U.S. Centers for Disease Control and Prevention (CDC) are monitoring samples from international passengers arriving in the U.S. after data collection got reduced when the pandemic measures were eliminated.

The Traveler-Based Genomic Surveillance program, launched by the CDC in late 2021, continues to operate in seven of the busiest international airports in the U.S. These airports include John F. Kennedy International Airport (JFK), Newark Liberty International Airport (EWR), San Francisco International Airport (SFO), Hartsfield-Jackson Atlanta International Airport (ATL), Los Angeles International Airport (LAX), Seattle-Tacoma International Airport (SEA), and Washington Dulles International Airport (IAD).

Partnering with XpresCheck, a company initially known for running airport spas but later involved in COVID-19 testing, CDC officials meet passengers from selected international flights after customs clearance. Officials request voluntary nasal swabs from the passengers, which are then pooled and tested by Ginkgo Bioworks, the CDC's lab partner.

Dr. Cindy Friedman, chief of the travelers' health branch at the CDC, emphasized the criticality of this program for early detection and filling in blind spots in global surveillance. As testing decreases in many countries, including the U.S., tracking passengers from abroad becomes an ideal method to monitor virus changes and global movement. Dr. Friedman herself participated in the program after returning from a trip abroad, underscoring the role of travelers as sentinels carrying valuable samples to the U.S.

"This program is critical for early detection and filling in many blind spots in global surveillance. This is really critical right now as many countries, including the U.S., are decreasing testing by as much as 90%. It's a key piece of biosecurity," Dr. Friedman was quoted as saying by TIME.

CDC officials select flights for testing each week based on global case trends. During the recent surge in cases in China and other parts of Asia, the program detected an increase in positive tests from the region just before case numbers peaked. The program often identifies case increases before they are reported in news stories or the public-health community.

To date, over 200,000 passengers have provided samples upon arrival in the U.S. Passengers offer anonymous information such as age, travel itinerary, and COVID-19 infection and vaccination history. They also provide two nasal swabs, with one added to a pooled sample and the other stored for potential later testing.

If the pooled sample tests positive, the second sample is individually tested to identify the positive cases within the pool. If novel changes are found in the genetic sequence, the second sample is sent to CDC labs in Atlanta for further characterization and added to the agency's growing database of SARS-CoV-2 sequences.

In 2021, the program detected the Omicron BA.2 and BA.3 variants one week and six weeks ahead of reported cases in the U.S., respectively.

While the program has received an impressive number of volunteers willing to provide nasal swabs, maintaining this altruism may become more challenging as the urgency of the pandemic diminishes. Therefore, the CDC is strengthening its airport wastewater testing program as a potential screening method.

For about a year, the agency has collected wastewater directly from lavatories on overseas flights at three to four airports, as well as from communal drains at SFO. Initial testing has shown that wastewater reflects the same variants identified through nasal swab testing, a finding supported by similar studies in Australia.

Wastewater screening holds promise as a permanent pathogen screening tool that can be adapted to detect any emerging disease-causing agent, making it crucial in preparing for future biological threats.

Health officials emphasized the importance of learning from the program's success and ensuring that the lessons are not wasted, particularly as precautions are being relaxed. Implementing anticipatory and proactive surveillance tools, such as wastewater screening, could have significantly benefited the world in early 2020 by detecting new strains of the coronavirus in multiple countries after its initial detection in China. This foresight would have facilitated the development of diagnostics, identification of outbreaks, and ultimately, changed the game.