Did Predeparture COVID-19 Testing Work? Evidence From Four U.S. Airports, 2022

The question

From December 6, 2021, anyone boarding a flight to the United States had to show a negative SARS-CoV-2 test taken no more than a day before departure, or proof of recovery from COVID-19 in the previous 90 days. On June 12, 2022, the requirement ended, though CDC still recommended testing. Modeling studies had estimated that testing the day before or the day of travel cuts transmission or importation by 31%–76%. Did it work in practice?

How it was studied

CDC's Traveler-based Genomic Surveillance Program watches for new SARS-CoV-2 variants among international travelers.

• Volunteers: adults arriving at Newark Liberty, John F. Kennedy, Hartsfield-Jackson Atlanta and San Francisco international airports gave a nasal swab and answered a survey, including whether they had tested before departure, and how.
• Pooling: swabs were pooled — 5 to 25 per pool — by the flight's country of origin, and tested by RT-PCR.
• Two periods: March 20–June 11, 2022, when predeparture testing was required, and June 12–September 3, 2022, when it wasn't.
• Adjustments: results accounted for COVID-19 incidence in each flight's country of origin, pool size and airport.

The results

• Who tested: 28,056 travelers from 24 countries, in 3,049 pools. With the rule in place, 79.1% reported a predeparture test; afterward, only 16.1%. Of those who said which kind, 69.1% had taken an antigen test.
• Positive pools: 17.9% during the requirement, 28.0% after it — a 56% increase that showed up across countries, airports, incidence levels and pool sizes.
• The adjusted effect: with the requirement in place, pools were 52% less likely to test positive (adjusted odds ratio 0.48). The finding held using 4- and 8-week windows around June 12.

Travelers reporting a predeparture test, and pools testing positive on arrival, March 20–September 3, 2022. Figure from the CDC report.

What it means

Testing before travel can cut the number of infectious travelers, and with it transmission in airports, on aircraft and in destination communities. The results matched earlier models. CDC continues to recommend testing before and after international travel, alongside isolation and masking. In December 2022, this analysis helped support a predeparture test requirement for travelers from China during a COVID-19 surge there.

Limits: volunteers may not represent all travelers; pooling hides individuals; some travelers connected from other countries; reported incidence may understate risk as testing declines; and some travelers skipped tests while required (such as recent COVID-19 cases), while others tested voluntarily afterward — which, if anything, would shrink the measured effect.

Adjusted odds of a positive pool across time windows before and after June 12, 2022. Figure from the CDC report.

Sources

Based on Stephen M. Bart, Teresa C. Smith, Sarah Anne J. Guagliardo, Allison Taylor Walker and colleagues, "Effect of Predeparture Testing on Postarrival SARS-CoV-2–Positive Test Results Among International Travelers — CDC Traveler-Based Genomic Surveillance Program, Four U.S. Airports, March–September 2022," MMWR, Centers for Disease Control and Prevention; a work of the United States government in the public domain.