The Centers for Disease Control and Prevention significantly revised its model of the breakdown of Covid-19 variants on Tuesday, estimating the Omicron strain accounted for about 58.6 percent of U.S. cases as of Dec. 25.
The public health agency’s previous estimate that the rapidly spreading variant accounted for 73.2 percent of cases nationwide on Dec. 18 is now revised down to 22.5 percent — a significant drop that falls outside the agency’s earlier 95 percent prediction interval, or likely range where future analysis will fall, of 34 to 94.9 percent of all cases.
The agency said the disparity was due to the rate with which the highly transmissible Omicron spread.
“There was a wide predictive interval posted in last week’s chart, in part because of the speed at which Omicron was increasing,” CDC spokesperson Jasmine Reed told POLITICO. “We had more data come in from that timeframe and there was a reduced proportion of Omicron.”
The White House didn’t immediately respond to request for comment.
The CDC’s revised Dec. 25 model includes a narrower confidence range of Omicron’s prevalence: 41.5 to 74 percent. The agency’s current model suggests that the Delta variant still represents 41.1 percent of U.S. infections. CDC updates the model weekly.
“Setting aside the question of how the initial estimate was so inaccurate, if CDC’s new estimate of Omicron prevalence is precise then it suggests that a good portion of the current hospitalizations we’re seeing from Covid may still be driven by Delta infections,” former FDA Commissioner Scott Gottlieb tweeted Tuesday.
The U.S. is now recording more than 206,000 daily Covid-19 infections — a number that is rapidly growing. Americans continue to travel at high levels through the holidays: more than 2 million people flew yesterday, according to Transportation Security Administration data.
“It’s important to note that we’re still seeing steady increase in the proportion of Omicron,” Reed said.