Friday, November 25, 2022

CDC Nowcast: BA.5 Continues To Decline As BQ.1/BQ.1.1 Ascend & 1st Appearance XBB



The latest CDC Nowcast has been released and BA.5, which became dominant in the United States in mid-summer, continues to give way to the Omicron tag-team of BQ.1/BQ.1.1, while the field expands further with the first mention of the XBB subvariant (a recombinant of BA.2.10.1 and BA.2.75 sublineages) which has been widely reported in Asia. 

These numbers are estimates based on limited surveillance, and previous week's numbers are often revised, meaning that even though this is the first mention of XBB, today's graphic shows it has been circulating here at very low levels for several weeks. 

So far, we've not seen any evidence that any of these new variants cause more severe illness than earlier Omicron strains, but many are not yet at a level that would send a strong signal.

We continue to see an erosion in our armamentarium of effective monoclonal antibody treatments, however, and the duration and degree of protection from current vaccines against these emerging variants remains to be seen.

Right now COVID is having to compete with the early arrival of RSV and influenza, and a process known as `viral interference' may be inhibiting some of its spread (see EID Journal Perspective: Viral Interference Between Respiratory Viruses).

How much of an impact that may be having, and how long it might last, remain to be seen.

BQ.1 and BQ.1.1 are currently poised to be the dominant strains in the US this winter, but with XBBBN.1, and BA.2.75 all gaining ground, it impossible to say what the COVID landscape will look like 90 days from now.