C.D.C. Airport Surveillance Found the First Known U.S. Case of BA.2
Eligible travelers could voluntarily submit a self-taken nasal swab at the airport.
Between September 29 and January 23, 10 percent of the 161,000 eligible travelers participating in the study and 1,454 sample pools were tested for the virus. Despite requiring pre-flight testing, more than 15 percent of collections tested positive.
This relatively high positivity rate may indicate that travelers became infected early – and therefore had too low a viral load to be detected by some tests – when they were tested before departure or contracted the virus in the time interval between tests. And landing in the United States, the researchers say. People may also have provided fraudulent test results.
The researchers found that until November 28, almost all pools of positive samples contained the delta variant. (The only exception was a positive sample, whose exact IT could not determine genetic origin.)
However, Omicron quickly became dominant after this; from November 28 to January 23, two-thirds of the positive samples were for Omicron. Most of the Omicron samples were a sub-variant of BA.1, initially the most common version worldwide. BA.1 remains the most common lineage in the United States, although BA.2 is gaining ground and currently accounts for 35 percent of infections. CDC estimates.