#16,621
Surveillance, reporting, and the frequency of genomic sequencing of COVID samples varies greatly between states, which makes it difficult to get a good handle on the national prevalence of a new, but still relatively low-level variant, like Omicron BA.2.
Since the first week of February (see CDC Nowcast: Omicron BA.2 Beginning To Show Up) the CDC has been reporting on its estimated prevalence, but each week since then we've seen major revisions to earlier estimates.
Last week, BA.2 prevalence was thought to be about 8.3%, but today we see that estimate has been revised to 6.6%, and this week's new estimate set at 11.6%. As the map above shows, incidence of BA.2 ranges from about 6% in the south and midwest to 24% in New England.
This variant is still gaining ground, but not as rapidly as previously estimated.
For now, BA.1.1 remains dominant, but if BA.2 performs as it has in other countries, it is expected to eventually over take it. Assuming something more `biologically fit' doesn't emerge in the meantime.
Despite some alarmist media coverage, we've not seen clear evidence that BA.2 produces more severe illness than BA.1.1, but it does appear to have an advantage in transmission. That said, data on Omicron BA.2 is still limited.
Given the limits of surveillance, testing, and genomic sequencing around the country, all of these numbers should be viewed as rough estimates - and as we've seen frequently over the past few weeks - are subject to revision.
