CDC Airport Surveillance Finds First Known Case of BA.2 in the US


Eligible travelers can volunteer to provide a self-collected nose swab at the airport. Swabs from five to 25 passengers from the same flight or country were added to a single tube and then tested for the virus using PCR testing. Positive samples were then sequenced to determine which version of the virus was present.

Between September 29 and January 23, 10 percent of the 161,000 eligible travelers were enrolled in the study, and a pool of 1,454 samples were tested for the virus. Despite the preflight testing requirement, more than 15 percent of the pools were positive.

This relatively high rate of positivity may indicate that passengers are in the early stages of their infection when they do their pre-departure test and therefore have viral loads that are too low for some tests to detect or have contracted the virus in the time between being tested. and landing in the US, say the researchers. People may also have submitted fake test results.

Before November 28, the researchers found that nearly all of the positive sample pools contained the Delta variant. (The only exception was a positive specimen whose exact genetic lineage could not be determined.)

But after that, Omicron quickly dominated; Between November 28 and January 23, two-thirds of the positive samples were Omicron. Most of the Omicron samples were originally the BA.1 sub-variant, which was the most common version worldwide. BA.1 remains the most common strain in the United States, but BA.2 is gaining ground and now accounts for 35 percent of infections. According to CDC estimates.

However, the researchers did find the BA.3 subvariant in a pool of samples collected from travelers from South Africa on Dec. They reported the finding on December 22 in GISAID, an international repository of viral genomes. It was the first reported case of BA.3 in the United States; it would be more than a month before the next one is reported.

The airport program also detected the first known case of BA.2 in the US in samples collected from South African travelers on 14 December. The researchers reported the finding a week before the next BA.2 case in the US was reported.

Dr. “This is a new tool in the CDC toolkit that works, and we’ve shown it’s effective and can be layered with all of our other mitigation measures,” Friedman said.



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