CHICAGO (WLS) -- The first instance of the omicron subvariant has been detected in Illinois, officials said Monday.
The case was discovered in a Chicago resident, who was tested nearly two weeks ago.
There's been a dramatic fall in new COVID infections across 40 states and territories, but now doctors are watching closely, as yet another variant has popped up.
Cases nationwide are down 32% since the peak of the omicron surge.
But the new threat is a mutation of omicron, dubbed BA.2.
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Doctors at Northwestern Memorial Hospital are looking at international data about this newest subvariant -- the worry is it may slow down decreasing numbers.
"Denmark, the United Kingdom, India, all of those countries have seen BA.2 come in, and while cases didn't surge, the amount that the case counts declined slowed," said Dr. Judd Hultquist, with the Feinberg School of Medicine at Northwestern.
Before it was detected in Illinois, scientists had tracked the subvariant to at least 29 states, accounting for less than 1% of all COVID cases in the United States.
British researchers found the vaccines appear to be effective against it.