Eligible vacationers may volunteer to supply a self-collected nasal swab at the airport. Swabs from 5 to 25 vacationers — from the similar flight or nation — have been added to a single tube after which examined for the virus utilizing P.C.R. testing. Positive samples have been then sequenced to find out which model of the virus was current.
Between Sept. 29 and Jan. 23, 10 % of 161,000 eligible vacationers enrolled in the examine, and 1,454 pattern swimming pools have been examined for the virus. Despite the preflight testing requirement, greater than 15 % of the swimming pools have been constructive.
This comparatively excessive positivity fee might point out that vacationers have been early in the course of their infections — and thus had viral masses too low for some exams to detect — after they took their predeparture exams, or that they contracted the virus in the time between being examined and touchdown in the United States, the researchers say. People may additionally have submitted fraudulent take a look at outcomes.
Before Nov. 28, almost all of the constructive pattern swimming pools contained the Delta variant, the researchers found. (The solely exception was a constructive pattern whose actual genetic lineage couldn’t be decided.)
After that, nonetheless, Omicron shortly got here to dominate; from Nov. 28 to Jan. 23, two-thirds of the constructive samples have been Omicron. Most of the Omicron samples have been the BA.1 subvariant, which was initially the most prevalent model worldwide. BA.1 stays the most typical lineage in the United States, although BA.2 has been gaining floor and now accounts for 35 % of infections, according to C.D.C. estimates.
But the researchers found the BA.3 subvariant in a pool of samples collected from vacationers arriving from South Africa on Dec. 3. They reported the discovering in GISAID, a world repository of viral genomes, on Dec. 22. It was the first reported case of BA.3 in the United States; it could be greater than a month earlier than the subsequent was reported.
The airport program additionally detected the first known U.S. case of BA.2, in samples collected from South African vacationers on Dec. 14. The researchers reported the discovering per week earlier than the subsequent U.S. case of BA.2 was reported.
“This is a new tool in the C.D.C. tool kit that works, and we’ve shown it’s effective and it can be layered with all of our other mitigation measures,” Dr. Friedman mentioned.