Why hasn’t the U.S. found more Omicron cases?

Last Friday, just a day after South African scientists first announced the discovery of the Omicron variant, Europe reported its first case: The new coronavirus variant was in Belgium. Before the weekend was out, Australia, Britain, Canada, Denmark, Germany, Israel, Italy and other countries had all found cases.

But in the United States, scientists kept searching.

“If we start seeing a variant popping up in multiple countries across the world, usually my intuition is that it’s already here,” said Taj Azarian, a genomic epidemiologist at the University of Central Florida.

On Wednesday, American officials announced that scientists had found it — in a California patient who had recently returned from South Africa. By then, Canada had already identified six cases; Britain had found more than a dozen.

The United States identified a second case, in Minnesota, on Thursday, and more are almost certainly lurking, scientists said. So why haven’t we found them yet?

Multiple factors may be at play, including travel patterns and stringent entrance requirements that may have delayed the variant’s introduction to the United States. But blind spots and delays in the country’s genomic surveillance system may have been factors, too, experts said. With many labs now conducting a targeted search for the variant, the pace of detection could quickly pick up.