The CDC's Weekly COVID Nowcast provides estimates based on limited surveillance, and previous week's numbers are often revised, meaning that they are most useful for spotting trends.
A prime example, last week's surprise debut of Omicron XBB.1.5 at 40.5% involved a major revision to several weeks worth of data to show this new variant first appeared in late November, and its rapid erosion of BQ.1/BQ.1.1 dominance.
The CDC's latest Nowcast backs off on that initial estimate. To be fair, data collection and reporting is primarily handled by the states - and between Thanksgiving and New Year's - is probably at its lowest ebb of the year.
Today the CDC has delivered a heavily revised estimate of XBB.1.5, which dramatically cuts last week's estimated prevalence from 40.5% to 18.3%, and now estimates it to be 27.6% for this week. An impressive gain week-over-week, but nowhere near the meteoric rise last week's report suggested.
The good news is that XBB.1.5 isn't quite the viral juggernaut that last week's report suggested. It is growing steadily, and will likely supplant the BQ variants in a matter of weeks, but - as the ECDC suggested earlier today - it may take a bit longer to spread internationally.
The caveat being, we could see additional revisions (up or down) to the data in the weeks ahead.
Assuming today's numbers are closer to reality, then we know a little less about XBB.1.5's impact than we thought, since its prevalence is roughly half of what we believed. That may make no difference in the end, but it does dilute its impact so far on hospitalizations and deaths.
Regardless of the variant leading the pack, we know that wearing a face mask can reduce your risks of contracting the virus, and the new bivalent COVID booster shot is believed to be more protective against severe illness (but not necessarily infection) than the older shot.
Stay tuned, COVID likely has more twists and turns in store for 2023.
