Note: The CDC website updated the graphic and chart moments after I posted this blog. I've replaced the old graphic with the new one, and have updated the text.
#16,807
Last week, in CDC Nowcast: BA.2.12.1 Edges Slightly Higher - B.1.1.529 Rebounds, I asked the rhetorical question; When will BA.4/BA.5 begin to appear in the weekly Nowcast?
The answer is today, with the first breakout of BA.4 and BA.5 appearing on the CDC's weekly Nowcast (see below). Over the past two weeks, both of these emerging variants have been `lumped' into the B.1.1.529 category.
As we've seen previously, this latest Nowcast has required the reshuffling of numbers from the past few weeks.
Given the limits of surveillance, testing, and genomic sequencing around the country, all of these numbers should be viewed as rough estimates, and we may see further revisions to the data in the weeks ahead.
As far as the significance of BA.4 and BA.5 - while both are Omicron offshoots - several studies suggest they have a transmissibility - and immune escape - advantage over BA.2 and BA.2.12.1.
Since isolates of these substrains were not readily available, they substituted lab-created chimeric recombinant SARS-CoV-2 viruses to approximate each subvariant, in order to conduct animal experiments. While infected hamsters (or mice, or ferrets) can provide valuable information, they aren't an exact analog for humans, and so that data must be viewed with a certain degree of caution.
Still, it would appear that BA.4 and BA.5 have a good shot at taking over from BA.2.x in the weeks ahead, and those who have recently recovered from BA.1 or BA.2 infection may find they have less immunity against reinfection than they would like.
