Friday, February 10, 2023

CDC COVID Nowcast: Omicron XBB.1.5 Now Estimated At 75% Of Cases In The U.S.


The CDC has released their latest COVID Nowcast, which suggests that the upstart CH.1.1 variant - which reportedly is outpacing XBB.1.5 in the UK - is losing ground to that dominant variant here in the states. 

XBB.1.5 is now estimated to make up about 75% of all cases in the United States, while CH.1.1 has slipped back to 1.3%.  Previously dominant BQ.1.x strains continue to lose ground as well. 

All of these numbers are estimates,revisions to previous week's numbers are common, and are more useful for spotting trends than nailing down exact percentages. The CDC has recently added the following caveat to their report.

Projections for an emerging lineage with a high growth rate may have a higher degree of uncertainty (wider predictive interval) when it is just beginning to spread and still has low weighted estimates. Projections may also be biased during times of delayed reporting (e.g., around holidays). CDC performs frequent evaluations of Nowcast to inform performance improvements.  

While XBB.1.5 is the viral king of the hill right now, we've seen a changing of the guard roughly every 3 to 4 months since Omicron emerged in late 2021.  Which means we can't predict with any certainty what strain will be in charge 90 days from now.