# Post #1416: COVID-19 trend to 1/27/2022, acceleration of trend.

Posted on January 28, 2022

Now that all the regions (and most states within each region) are on a downward trend, the decline in the U.S. new COVID-19 cases is accelerating.  Cases are down 20% in the past seven days, and we’re now more than 25% below the peak of the Omicron wave, at just over 180 new cases per 100K population per day.

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 1/28/2022, 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

Enough individual states have peaked that we can now clearly see the “arch” shape characteristic of a peak.

By historical standards, the number of cases is still astronomical.

That said, the average infection under Omicron is nowhere near as risky as it was under Delta.  Here are my latest estimates for the case hospitalization rate and case mortality rate under Delta and Omicron.  (Where the “case rate” is the number of events per formally diagnosed case.)  I calculate a crude mortality rate by comparing current deaths to new cases from two weeks ago, to account for the mean lag between infection and death for decedents.

Source:  Calculated from CDC COVID data tracker, counts of cases, hospitalizations and deaths.

If I focus narrowly on just the risk of hospitalization and death, then for the U.S. population as a whole, an Omicron infection is somewhere between (0.3/1.3 = ) 23% as risky (for death) to (3.0/7.5 = ) 40% as risky (for hospitalization), compare to Delta.

Let me just slur over that difference and say that, for the U.S. population as a whole, an Omicron infection is about one-third as risky as a Delta infection.  By the “population as a whole” I mean not just the demographics of the U.S. population, but also the current mix of unvaccinated, vaccinated, and boostered individuals, plus those who have and have not survived a prior COVID-19 infection.

Here’s a fun fact:  The case hospitalization and mortality rates in the 2020-2021 winter wave — before vaccines — were just about equal to the rates of the Delta wave — after vaccines.  Delta was far more virulent than the native (Wuhan) strain.  But that was (purely by chance) offset on average by the impact of a roughly 65% vaccination rate, yielding roughly the same population-average case rates.

The upshot is that for the population as a whole, each Omicron cases bears about one-third the risk of serious adverse events that the U.S. population faced from any of the prior strains.  That’s either the native (Wuhan) strain with no vaccinations, or the Delta strain with about a 65% vaccination rate.

So if I “risk adjust” the case numbers across the strains, accounting for the much lower risk that each Omicron case has, and factor in the rate at which Omicron took over from Delta, I get a chart that looks like this:

The bottom line is that the overall risk of hospitalization and death from COVID-19 are about the same this winter as they were last winter, for the average U.S. resident.  That, despite the vastly higher number of cases.

Somewhat higher risk of hospitalization:

Source:  CDC COVID data tracker, accessed 1/28/2022

Somewhat lower risk of death:

Source:  CDC COVID data tracker, accessed 1/28/2022

That’s the result of offsetting effects.  Much higher case count.  Much lower risk per case.

The kicker is that last year there were no vaccines, and we were more-or-less all in the same boat.  The average risk from last year was the average for everybody.  By contrast, this year, vaccination plus booster greatly reduces risk of infection, hospitalization, or death under Omicron.  The average boostered person actually faces considerably lower risk in the Omicron wave than they faced in the winter 2020/21 wave.