Now 22 new cases per 100K population per day, rounded to the nearest digit, up 22% in the past week. The latest strain — BA.2.12.2 — still is not yet the dominant strain in the U.S. Deaths still are not rising.
Data source for this and other graphs of new case counts: Calculated from The New York Times. (2021). Coronavirus (Covid-19) Data in the United States. Retrieved 5/10/2022, from https://github.com/nytimes/covid-19-data.” The NY Times U.S. tracking page may be found at https://www.nytimes.com/interactive/2020/us/coronavirus-us-cases.html
Source: CDC COVID data tracker.
Since the start of this latest COVID-19 wave (the BA.2.12.2 wave), cases are up 150 percent, hospitalizations are up 50%, and deaths are down 50%. The calculated average length of stay (per COVID-19 case) is well under 5.5 days now.
Source: Calculated from CDC COVID data tracker.
A common mis-interpretation of the data
You might start thinking that this latest version (BA.2.12.2) is “weaker” than Omicron (BA.2) itself. You can see numerous popular press articles that naively look at the raw numbers and say exactly that.
I think that’s incorrect.
Sure, average cases severity appears to be declining. But I don’t think that has anything to do with changes in COVID-19.
Instead, I think this is a consequence of the increasing share of cases occurring among the vaccinated. At this point — well after the last wave of booster shorts — vaccine and booster do little to prevent an individual from having any COVID-19 infection. But they still work quite well to prevent severe infections. Here’s a CDC graphic I’ve shown before:
Source: CDC COVID data tracker.
As a consequence of that loss of immunity against any infection, the vaccinated and boostered will now make up a larger share of all new cases. So a larger fraction of the infected population has vaccination-acquired resistance to severe infection. And so, per observed case, severity is declining.
That doesn’t mean “the virus is getting weaker”. It just means that vaccination is now working mostly to reduce severity, not to prevent illness. And by drawing an increasing share of the vaccinated into the overall pool of reported infections, the average observed severity of illness is falling.
Unfortunately, the CDC’s data split by vaccination status is ancient. The most recent observation is from the end of February. At that point, for sure, the case mortality rate for Omicron, for the unvaccinated, was two percent. That is, as of the end of February, Omicron was still killing one-in-fifty of unvaccinated individuals with a reported infection.
The only point I want to make from the chart above is that even a modest shift in the mix of vaccinated and unvaccinated among new infections could account for a declining case mortality rate. (And, for that matter, a reduced hospitalization rate).
