Tuesday, April 26, 2022

CDC Nowcast: BA.2.12.1 Continues To Erode BA.2's Dominance


For the 4th time in just under 5 months we are watching the dominant strain of COVID give way to a newer, more transmissible variant here in the United States. 

Last November, Delta still held sway in North America, but it was replaced in December by Omicron B.1.1.529, which in turn gave way to BA.1.1 in January.  By mid-March BA.2 wrested control from BA.1.1, and now we have BA.2.12.1 rapidly gaining on BA.2.

The latest Nowcast from the CDC shows BA.2 still the dominant strain, but its share has dropped from 75.9% two weeks ago to 68.1% this week.  BA.1.1 has dropped to under 3%, and B.1.1.529 is barely measurable at .2%

BA.2.12.1, while still only at 28.7% nationally, already accounts for nearly 60% of cases in HHS region 2 (New Jersey, New York, and the U.S. territories in the Caribbean), and clearly shows its aggressive trajectory. 

Given the limits of surveillance, testing, and genomic sequencing around the country, all of these numbers should be viewed as rough estimates. But they do suggest that BA.2.12.1 could become dominant in the United States in the weeks and months ahead.

Assuming (as always) that something more biologically fit doesn't emerge in the meantime.

While we don't have any evidence that BA.2.12 produces any greater severity of illness than BA.2, we are seeing an increase in cases around the country. Hospitalizations and deaths are always lagging indicators, and so we'll be watching these numbers closely. 

It has only been 2 weeks since the NY State DOH Statement on Omicron Subvariants BA 2.12 and BA.2.12.1 raised concerns, and only 1 week since Omicron Subvariant BA.2.12.1 Mades Its 1st Appearance in the CDC Nowcast. 

But as the chart below illustrates, this new variant is rapidly making strides here in the United States.  In other parts of the world, there are yet other variants (e.g. BA.5 and BA.5) making moves, which we are also watching. 

While we've been very lucky in that none of these emerging Omicron variants has brought with it increased severity or mortality, it is concerning to see how quickly these new, `biologically fit' variants are emerging.