XBB.1.1.6 Nowcast Estimates.
#17,408
The CDC's COVID Nowcast has been remarkably stable for the past couple of months, with XBB.1.5 making up roughly 90% of all COVID cases in the country, and very few signs of any competition by the other half dozen or so variants in the mix.
Omicron variants have a history of remaining dominant for only a few months, only to be replaced by something more `fit', and so we've been on the lookout for the next contender.
While it had yet to be reported officially in the United States, yesterday in Preprint: Virological characteristics of the SARS-CoV-2 Omicron XBB.1.16 variant, we looked at a possible heir apparent which has been making inroads in India, and a few other countries around the world.
The authors suggested that XBB.1.16 might be the next variant to watch, writing:
Altogether, our data suggest that XBB.1.16 has a greater growth advantage in the human population compared to XBB.1 and XBB.1.5, while the ability of XBB.1.16 to exhibit profound immune evasion is comparable to XBB.1 and XBB.1.5.
Today's Nowcast from the CDC reports for the first time that XBB.1.16 is present in the United States - and has been for several weeks - and it appears to be making significant gains against XBB.1.5 in several areas of the country, most notably in the south (region 6 est. 21.3%).
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.
Debuting impressively in 2nd place, XBB.1.16 could be on track to dethrone XBB.1.5 from the top spot in the weeks ahead.
Exactly what that means in terms of impact is difficult to say. Somewhat reassuringly, we've not seen any evidence that XBB.1.16 produces any greater severity of illness than earlier Omicron variants, but that is based on limited data.
But another surge - even of a relatively mild variant - could produce significant morbidity and increased mortality, so we'll be watching its progress closely in the weeks ahead.
