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The Centers for Disease Control and Prevention estimated that the Omicron variant now accounts for about 59 percent of all Covid cases in the United States, a significant decrease from the agency’s previous estimate. The update shows how difficult it is to follow the rapidly spreading variant in real time and how poorly the agency has communicated its uncertainty, experts said.
Last week, the CDC said that for the week ending December 18, Omicron made up about 73 percent of the variants in circulation in the United States. However, in its revision, the agency said the variant made up about 23 percent of the cases this week.
In other words, Delta, which has dominated U.S. infections since summer, was still ruling the United States this week. That could mean a significant number of current Covid hospital admissions from Delta infections, Dr. Scott Gottlieb, a former commissioner for the Food and Drug Administration. recommended on twitter. Hospital stays are usually several weeks behind the first infections.
Experts said they weren’t surprised by the revisions because the CDC’s estimates are rough estimates with a wide range of possible values ​​known as “confidence intervals”. Cases of Omicron can only be confirmed through genetic sequencing, which is only performed on a subset of samples across the country.
And Omicron is still spreading extremely quickly.
Still, they said the CDC did a poor job communicating the uncertainty of their estimates. The agency had a number of missteps during the pandemic, including sending botched tests out early and changing the masking instructions. When the recommended isolation time for those who tested positive but showed no symptoms cut in half to five days on Monday, critics argued that no testing was required before returning to work.
Dr. Jerome Adams, who served as the US surgeon general under former President Donald J. Trump, wrote on Twitter on Tuesday that although he respects the CDC, he does not agree with their decision on isolation times.
I love the CDC. Grown up wanting to work there and was one of their most ardent defenders.
I never dreamed that the day would come when I would advise people NOT to follow their lead. Break my â¤ï¸
But ask one of them. They wouldn’t even obey it for their own family. https://t.co/qm1yD4U7pR
– Jerome Adams (@JeromeAdamsMD) December 28, 2021
He also criticized the lack of a test option or recommendation for higher quality masks in the new instructions.
David O’Connor, a virologist at the University of Wisconsin-Madison, said of the Omicron estimate, “The 73 percent got a lot more attention than the confidence intervals, and I think this is one of many examples that scientists are trying to to project an air of confidence about what will happen. “
Dr. O’Connor said he found the initial estimate “high” at first. The agency made the estimate based on a “relatively small number of sequences,” he added.
“It’s like playing Name That Tune and trying to tell by the first note whether the song is ‘Ice Ice Baby’ by Vanilla Ice or ‘Under Pressure’,” said Dr. O’Connor. “Without more data, it can be really hard to know which one it will be.”
The new estimate of 59 percent is also a rough calculation, said experts and is expected to be revised in the coming weeks.
“I just want people to be very aware that this is an estimate that doesn’t really come from sequence-confirmed cases,” said Nathan Grubaugh, an epidemiologist at the Yale School of Public Health. “At Omicron in particular, it was very difficult to make forecasts because things change so quickly.”
Dr. Grubaugh, who is tracking likely Omicron samples in Connecticut, said the variant accounts for more than 80 percent of cases there, but also points out that the country is heterogeneous and the variant is likely to have different prevalence in different locations.
“I don’t know how the CDC built their algorithm, but people created these programs, and people are fallible,” said Massimo Caputi, molecular virologist at Florida Atlantic University School of Medicine. “Ultimately, you can predict as much as you want, but you have to look at the numbers you have in your hand.”
Dr. O’Connor, who is tracking Omicron in Wisconsin, said the variant accounted for half of the cases on the University of Wisconsin-Madison campus in just three days. “When I did a bet prediction, it wasn’t so much that the number 73 percent was wrong, but the timing to get there was wrong,” he said.
These predictions are likely to become more accurate over time as more data is collected about Omicron.
More accurate numbers are needed to intelligently distribute Covid treatments. One of Omicron’s major challenges is the variant’s ability to thwart two of the three monoclonal antibody treatments that can prevent serious illness in Covid-19 patients. As a result, some hospitals have started reducing these treatments; Administrators from New York-Presbyterian, NYU Langone and Mount Sinai all said they would stop giving patients the two treatments that are ineffective against Omicron. But the drugs could help people infected with Delta.
“If you’re still having these Delta cases, going off monoclonals means that all of the people who would have benefited from them won’t get them at all,” said Dr. O’Connor.
Dr. O’Connor said scientists and healthcare providers need to better communicate the uncertainty in the predictions they share with the public. “It will be really important to have the humility to acknowledge that there is much that nobody knows and does not know right now.”
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