Omicron isn’t overtaking Delta as quickly as the CDC thought—and that’s bad news

Omicron is not infecting people at the rate officials thought.
A doctor in a protective suit taking a nasal swab from a person to test for possible coronavirus infection
Testing may not show the full picture of when a surge peaks. zstockphotos/Deposit Photos

COVID-19 case rates in the US are swelling, and the highly infectious Omicron variant is raising alarms around the world. But the US Centers for Disease Control and Prevention (CDC) now says that the number of infections caused by Omicron in the US were highly overestimated. 

The CDC previously reported that the Omicron variant was responsible for about 73 percent of new COVID-19 infections between December 12 and 18.. However new data released by the CDC on Tuesday show a revised estimate for that week of just 23 percent, a 50 point drop. In the most recent week of data, December 19 through 25, the CDC estimates that Omicron made up about 59 percent of infections—almost all other cases were caused by Delta.

While Omicron is clearly a variant of concern, these data show that its rate of infection was not as high as health officials initially believed. The Delta variant, which tends to cause more severe illness compared to earlier strains, is clearly still a large driving force in the continuation of the coronavirus pandemic. 

“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,” Scott Gottlieb, former commissioner of the Food and Drug Administration, posted on Twitter.

The inaccuracy of the CDC’s initial overestimates illustrate how lag time in collecting infection data from tests can skew numbers. “There’s no way around it, it is a huge swing that makes it seem like something went really wrong,” Shruti Gohil, associate medical director for epidemiology and infection prevention at UC Irvine’s School of Medicine, told NPR. “But there is always a delay in the testing information that comes in, and that’s what the public should take away.”

Data on new case counts are likely also unstable given the holiday season, CDC spokesperson Jasmine Reed told Politico. Lagging state reporting and testing backlogs are to be expected, and she added that “the counts of cases will become more stable after the new year.”

It’s important to note that the CDC’s slashed estimates of Omicron does not mean that ‘Omicron is not that bad,’ Gohil told NPR—it’s “still too early to really know even that.” Rather, this should serve as a reminder that “Delta is the beast that you should be worried about.” 

The latest data from the CDC and the US Department of Health & Human Services (HHS) show that Omicron has the highest prevalence in HHS Region 2 which includes New Jersey, New York, Puerto Rico, and the Virgin Islands (88 percent of all COVID cases); and Region 6 which includes Arkansas, Louisiana, New Mexico, Oklahoma, and Texas (87 percent). Delta is still responsible for more than 70 percent of cases in HHS Region 7, which covers Iowa, Kansas, Missouri, and Nebraska; and more than half of infections in Region 1 which includes Connecticut, Maine, Massachusetts, New Hampshire, Rhode Island, and Vermont. 

With the Delta variant still circulating, Gohil told NPR that now is not the time to be lax with pandemic preventative measures, like masking and distancing. “The bottom line is,” she said, “don’t take your masks off just yet and get vaccinated, vaccinated, vaccinated, vaccinated—and boosted.”