CDC revises XBB.1.5 estimates; admissions jump 16% in 1 week — 10 COVID-19 updates

The CDC has lowered its estimate of omicron subvariant XBB.1.5's prevalence in the U.S., now saying the highly transmissible strain accounts for about 28 percent of COVID-19 cases. 

The CDC first started tracking XBB.1.5 separately from its parent strain XBB the week of Dec. 31, estimating it accounted for about 4 percent of cases nationwide. Because of the strain's fast growth rate, CDC modeling forecasted that the strain would account for about 41 percent of cases by the end of December. 

"But projections can be uncertain when a variant is just beginning to spread. When Nowcast predicted XBB.1.5 at 41 [percent], there was a wide prediction range of about 23 [percent] to 61 [percent]," the CDC said in a Jan. 6 report. "Since then, more data have come in from mid-December, as well as additional data delayed by the holidays."

Based on this new information, the CDC revised its estimate on XBB.1.5's prevalence from 41 percent to 18 percent for the week ending Dec. 31. 

The revised proportion is lower than previously thought and means the new strain is not yet dominant in the U.S. Still, the subvariant's prevalence is growing quickly, jumping to 28.4 percent in the week ending Jan. 7, the CDC said. Omicron subvariant BQ.1.1 remains the nation's dominant strain, accounting for 34.4 percent of cases. 

The lower estimate leaves "more runway before this variant achieves dominance cross country," Eric Topol, MD, founder and director of Scripps Research Translational Institute in San Diego, wrote in a Jan. 6 tweet responding to the revision. 

Eight more updates from the CDC's COVID data tracker weekly review:


1. As of Jan. 4, the nation's seven-day case average was 67,243, a 16.2 percent increase from the previous week's average. 


2. The seven-day hospitalization average for Dec. 28 to Jan. 3 was 6,519, a 16.1 percent increase from the previous week's average. 

Community levels 

3. As of Jan. 5, 19.5 percent of counties, districts or territories had high COVID-19 community levels, 41.9 percent had medium community levels and 38.5 percent had low community levels. 


4. The current seven-day death average is 390, up 8.3 percent from the previous week's average. Some historical deaths have been excluded from these counts, the CDC said. 


5. As of Jan. 4, more than 229.3 million people — or 69.1 percent of the population — have completed their primary vaccination series.

6. More than 48.2 million, or 15.4 percent of the population ages 5 and older, have received an updated booster dose. 

Wastewater surveillance 

 7. About 80 percent of U.S. testing sites are reporting moderate to high virus levels in wastewater. Of these surveillance sites, 58 percent are seeing some of the highest levels since Dec. 1, 2021. 

 8. About 56 percent of sites are reporting an increase in virus levels, and 33 percent of sites are seeing a decrease.

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