#16,821
Last week the CDC released their 1st COVID Nowcast that broke out the emerging BA.4 (5.4%) and BA.5 (7.6%) Omicron variants from the background clutter of minor strains, and showed the dominant BA.2.12.1 has having risen to only 62%.
Today's Nowcast shows nearly a doubling of BA.5 across the country (now 13.3%), and a roughly 50% increase in BA.4 (now 8.3%) while BA.2.12.1 eked out about a 4% gain over last week.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.
BA.2 continues to be the biggest loser, having fallen from > 50% of cases 5 weeks ago to just 14.2% now.
As far as the significance of a BA.4 / BA.5 wave - while both are Omicron offshoots - several studies suggest they have a transmissibility - and immune escape - advantage over BA.2 and BA.2.12.1.
Thus far, we've seen no credible evidence that either produce more severe illness than BA.1/BA.2, although some laboratory animal studies have hinted at that possibility.
It appears increasingly likely that BA.4 and BA.5 will replace BA.2.12.1 as the dominant strains in the United States in the weeks ahead - and like Europe - will face a surge in cases.
BA.4 and BA.5's transmissibility appears to be based primarily on its ability to evade the protective effects of prior infection (with BA.1/BA.2) and vaccination.
Although vaccine breakthrough infections appear likely, the evidence to date suggests that those who are vaccinated and recently boosted suffer less severe disease, and are less likely to be hospitalized or die, than those who are under-or-unvaccinated.
With a new, increasingly transmissible COVID variant rising to dominance every 6 to 8 weeks, the big unknown remains, what comes next?
At some point this rapid replacement cycle will end. But for now COVID doesn't appear ready to settle down into a reasonably stable endemic virus.
