COVID source callout: The CDC’s slow variant updates

Due to reporting delays, the CDC’s variant data fails to convey Omicron’s rapid spread through the country. Chart retrieved on December 19.

On Tuesday, the CDC updated the Variant Proportions tab of its COVID-19 data dashboard. This update included some alarming information: Omicron had jumped from causing about 0.4% of cases in the week ending December 4, to 2.9% of cases in the week ending December 11. In the New York and New Jersey area, it was causing 13% of cases.

At this rate of increase, we can anticipate that, as of yesterday (December 18), Omicron is already causing roughly 21% of cases in the U.S.—and more than 90% of cases in New York and New Jersey. But because of the CDC’s delayed updates, the majority of people who go look at the CDC’s dashboard anytime before its next update, this coming Tuesday, would likely presume that Omicron is still causing a tiny minority of cases.

I’ve written before about the delays in collecting and reporting coronavirus sequencing data. It can take weeks for a COVID-19 test sample to go from a patient’s nose to a nationwide sequencing database, which leads to inevitable lags in the U.S.’s genomic surveillance. This is understandable. But in a crisis moment, when Omicron is here and spreading rapidly, the agency should clearly label the lags and update its projections to provide a more accurate view of the variant’s growth. 

What’s more, the CDC’s data update on Tuesday was not communicated widely; Director Dr. Rochelle Walensky gave a TODAY Show interview, and that was about it.

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3 responses to “COVID source callout: The CDC’s slow variant updates”

  1. Omicron updates: A major surge is underway in the U.S. - Variants Avatar

    […] week, I wrote that the CDC’s estimates of new COVID-19 cases caused by different variants were providing a delayed, incorrect look at Omicron in the U.S. This past Monday, the ramifications of that delay were made clear: the CDC updated its […]

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  2. Omicron updates: ‘mild’ cases can still mean a nasty surge - Variants Avatar

    […] based on sequencing data that are reported with a lag of multiple weeks. And the agency’s slow pace of updates means that its estimates are unlikely to match the actual variant situation in the U.S. anyway. […]

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  3. Omicron updates: the surge is here, but peaks might be in sight - Variants Avatar

    […] December 25 and 38% Omicron for the week ending December 18. While these estimates continue to be based on weeks-old data, it the CDC now has enough sequencing information to make Omicron estimates with lower confidence […]

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