Author: chogan@directresearch.com

Post #1381: SNOVID-19.

I can’t help but smile when I hear the term “snow day”.  It’s a conditioned reflex, the result of having gone to school in the South.

But now there’s a new perspective on that old joy.  After a couple of years of complaining about hanging around the house and not doing much because of COVID, I now find that hanging around the house and not doing much because of snow is totally different.  It’s unironically fun.

Thus proving that mental attitude is all in your head.

It’s a snow day here in Fairfax County, VA

This is God’s way of shouting at us “Do Not Go Back to School”!  (That’s per a a friend of my wife’s, a schoolteacher who isn’t much looking forward to in-person classes with Omicron).

People from northern climates laugh at the degree of disruption a little snow causes in the South.  But, having seen it from both sides — grew up and live in Virginia, but spent several long, cold winters in Chicago — I can tell you that snow in the South is just a completely different beast from snow in the North.

It’s slipperier.  And that’s a fact.

Wintry mix is our favored form of precipitation this time of year.  It’s a random combination of snow, sleet, ice pellets, freezing rain, and rain.  The weather forecasters aren’t quite sure what will be hitting the ground at any particular moment.  The only thing they agree on is that whatever it is, you can slip on it.

(My wife often said that Baskin-Robbins should offer a flavor of  ice cream by this name.  It would come pre-marketed because everyone in this area hears that term all season long.)

We get wintry mix so often in this area because the temperature is typically just about freezing when it snows. Might get snow, might get rain.  You never know until it gets here and makes up its mind.

This morning, it’s 30 F with high humidity.  And so, we’re actually getting just snow.  It melts as it hits, then piles up, and as a result, we end up with a thin layer of slush everywhere, covered with snow.  That will be freezing to ice in random areas throughout the day, and will freeze uniformly tonight.  Tomorrow morning, anywhere that hasn’t been shoveled and salted will have a uniform coating of snow-over-ice.

Let me contrast this with a typical Chicago snowfall.  Typically, it’s 20F or so, everything is already frozen solid, and 4″ of powdery dry snow comes down.  It doesn’t melt.  It doesn’t stick to anything.  People sweep off their sidewalks and life moves on.

Having driven on roads in both areas, I’d trade their coefficient of friction for our coefficient of friction any day.

Finally, hills.  Midwesterners in general don’t have to cope with them.  For sure, they just plain don’t have them in Chicago.  Around here, though, they are a fact of life.  And once you find yourself sliding downhill, on the frozen slush hidden under the snow, there really isn’t much you can do about it.

Bottom line, I’m leaving the car in the garage today.  And the power has gone out now.  So I will just enjoy sitting around the house doing nothing.  For a change

 

 

 

Post #1380: Omicron, I sure got it wrong.

 

I expected the U.S. Omicron wave to be short, sharp, and with very low average case severity.  That’s what occurred in South Africa, and that’s what I expected to see here.

If we’d repeated the South African experience, we’d have peaked by now. 

Instead, the Omicron wave in America is continuing longer, and moving  higher, than it did in South Africa.  And average case severity for new cases, relative to Delta, is higher here than it was in South Africa.  As a result, what I thought was going to be a fairly benign wave of COVID in the U.S. is starting to show some potential for turning into a true disaster.

In short, the South African experience was not a good model for what’s happening in the U.S., and the U.K., and some other European countries.

What are some possible reasons for that?  Turning that around, what are some major differences between South Africa and the U.S. that might have caused the Omicron wave to have differed?

Delta never left us.

Let me start with the most obvious contrast between South Africa and the U.S./U.K./Europe.

South Africa had a “pure” Omicron wave, in the sense that there were almost no pre-existing Delta cases circulating in the country.  All you ever saw there, for their short, sharp wave, was Omicron.  As you can see, the daily new case count was practically zero prior to the start of their Omicron wave.

In the U.S., by contrast, we never really finished our Delta wave.  You can see a significant case count of Delta already occurring by the start of the U.S. Omicron wave.  The U.S. — and most of Europe — was already in the middle of a mild (U.S.) to quite severe winter (U.K.) wave of Delta, when Omicron came along.

 

We know that Omicron is displacing Delta as a fraction of all cases.  Here’s the most recent CDC estimate:

Source:  CDC COVID data tracker accessed 1/20/2022.

(This is something that I’ve puzzled over before.   Somehow, each new strain manages to kill off the prior strains.  Alpha displaced the native (Wuhan) strain, Delta displaced Alpha, and in each case, more or less 100% of new cases end up being the new strain.  The older strain disappears.  But the mechanism behind that has never been clear to me.)

So, Omicron has been displacing Delta.  Or has it?  Delta has been falling as percent of cases.  But what has it been doing in terms of the actual number of cases?

Let’s convert the CDC’s Omicron-as-a-percent-of-new-cases numbers above to actual counts of Omicron and Delta cases.  That’s easy enough to do — just multiply the total new case count by those variant percentages. (There are a few fine points of method here — I filled in the daily percentages using the week-to-week growth rates above, I slid the whole assembly of daily percentages back by three days prior to the listed end-of-week dates, and and so on.  Those were all obvious things to do if you’d thought about it for five minutes.)

And despite how obvious it was to do this, I got a pretty big surprise.  Through Christmas 2021, Omicron did not displace Delta, it mostly added on top of Delta.

Source:  Calculated from case counts as variant estimates from the CDC COVID data tracker.

Above, the orange line is my estimate for the count of new Delta cases.  As you can see, that hadn’t really budged, as of Christmas 2021.  Omicron accounted for more than half of new U.S. cases by Christmas.  But it did that by growing on top of a fairly stable population of daily new Delta cases.

As simple and obvious as this now appears, I haven’t seen this point made elsewhere yet.  So I wonder if this is a new phenomenon.  Maybe this is some unique consequence of Omicron being so vastly more contagious than Delta.  As some point, if I can dig up the data, I may want to go back and see what happened at the Wuhan/Alpha and Alpha/Delta transitions.

The upshot is that one major difference between South Africa and the U.S. is the Delta wave.  South Africa didn’t have one.  All they had to deal with was Omicron.  But as of Christmas 2021, in the U.S., that winter Delta wave has not gone away.  It’s still here, hiding beneath the Omicron wave.  If anything, it appears to be fading slowly.

Difference sources of COVID-19 immunity

Another glaring difference between South Africa and the U.S./European experience is the mix of sources of COVID-19 immunity within the population.  Roughly speaking, most of our immunity comes from vaccination, most of theirs comes from prior infection.  Approximately like this:

Sources of information:

U.S. percent with prior infection is the count of positive cases as of 12/15/2021, times 1.9 (based on the most recent seroprevalence data from CDC, to account for cases not formally diagnosed), divided by total U.S. population.  All the COVID data are from the CDC COVID data tracker.

U.S. percent fully immunized and boostered is from the CDC COVID data tracker as of 2/1/2022.

South African percent fully immunized is from Our World in Data, rounded down to 25%. 

South African percent with prior infection is from this analysis from this  undated PowerPoint from the South African National Institute for Communicable Diseases.

To be clear, Omicron appears to be able to infect both the fully-vaccinated and prior-infection populations easily.  That is, based on the South African experience, there were a lot of breakthrough infections (among fully-vaccinated) and reinfections (among those recovered from prior infection).

If there were some difference in protective ability, then that might influence the course of the Omicron pandemic in these countries.  But the bottom line is that there is no hard evidence one way or the other, on this point.  Near as I can tell, all the evidence says that neither prior infection nor full (two-shot) vaccination provides significant protection against Omicron.  Which one is the lesser of two zeroes cannot be determined from existing data.

In theory, this ought to be roughly knowable from population-based administrative data available in the U.S.  In U.S. states, on a person-by-person basis, state health departments know who has tested positive for COVID-19 in the past, and who has been vaccinated (partially, fully, or boostered).  From that, they can (and some do) flag cases that are breakthrough (in a fully-vaccinated person) and reinfection (in a person with prior positive test for COVID-19).  If there is some new, significant different in immunity across those populations, then the ratio of identified reinfections to identified breakthrough infections should change as the Omicron fraction of all infections rises.

There is no doubt that a state health department could do this analysis.  That said, as an outside, I have yet to find a state health department that has published the relevant, current data, let alone done the analysis.

Instead, I have to rely on various scholarly studies.  Near as I can tell, these boil down to:

  • Neither prior infection nor standard (two-dose) vaccination provides much protection against Omicron, if any.
  • Studies disagree whether or not prior infection or vaccination provides better immunity.
  • There’s enough uncertainty around the estimates that it’s probably not possible to answer this question from existing research data.

The first study comparing natural immunity and vaccine immunity against Omicron is a study of infection rates of persons in Great Britain, using data from the end of November into early December.  Based on their sample sizes, they are unable to rule out zero protection from Omicron, from either source of immunity.  Omicron.  As reported at this link, based on the original research as reported at this link:

The reinfection risk estimated in the current study suggests this protection has fallen to 19% (95%CI: 0-27%) against an Omicron infection.
vaccine effectiveness estimates against symptomatic Omicron infection of between 0% and 20% after two doses, and between 55% and 80% after a booster dose.

A different study, using in vitro assays of immune response, again found little response from either prior infection or full vaccination, but suggested that the prior infection response was, if anything less than that of antibodies from fully-immunized individuals.  That’s reported at this link, with the original research at this link.

Antibodies from people double-vaccinated with any of the four most widely used vaccines—Moderna, Pfizer, AstraZeneca, Johnson & Johnson—were significantly less effective at neutralizing the omicron variant compared to the ancestral virus. Antibodies from previously infected individuals were even less likely to neutralize omicron.

I’m going to give up on finding anything more definitive for now.  Near as I can tell, neither prior infection or full vaccination provides much protection against Omicron, if any.  It seems unlikely that any small difference in effectiveness between these two sources of immunity would be able create such a large difference between the U.S. and South African experience.

COVID hygiene.

The research above suggests that neither full vaccination nor prior infection provides any significant protection against Omicron.  The logical implication is that for the roughly 70 percent of the U.S. population that has not received a booster dose, the only thing that slows spread of Omicron is COVID-19 hygiene:  Wearing a high-quality mask, staying out of high-transmission-risk situations, and the like.

Restated:  If most of the population has virtually no immunity to Omicron, then differences in COVID hygiene can play a significant role in determining variations in Omicron spread across nations.

For the U.S., as I have shown repeatedly here, mask use has hardly changed over the past month, based on data from Carnegie-Mellon University.

Source:  Carnegie-Mellon COVIDcast.

It’s tough to find hard data on the extent to which South Africans increased use of masks.

News reporting makes it clear that they take mask mandates seriously.  (Thousands arrested for not wearing masks, dated Feb 2021).  I don’t believe I’ve ever heard of an American arrested or even fined for failing to wear a mask.  And, while South Africa is now lifting other restrictions, failure to wear a mask in public remains a criminal offense.

Historically, rates of mask use in South Africa appear to have been comparable to those in the U.S., based on self-reported survey data from the end of 2020.  That’s reported at this link.

I can’t seem to find objective data.  But the presence of a national law that makes it a criminal act to be outside the home without a mask — actually enforced with arrests and penalties — suggests a far more serious attitude in South Africa than in the U.S.

So this remains a guess, but I’m guessing that South Africans take mask wearing more seriously.  Certainly compared to a country with no national mask mandate, where state mandates seem to be completely unenforced by law officers, and where many states have chosen to prevent localities from passing their own mask mandates.

Summary.

There’s no simple answer as to why South Africa’s experience with Omicron has been so vastly better than our own.

In part, we were already burdened with Delta, and we continue to be burdened with that.  But that, by itself, wouldn’t explain prolonged growth of Omicron here, compared to South Africa.  More total cases, perhaps, but not more growth.

In part, prior pandemic waves seem to have been somewhat shorter, consistent with the U.S. being a geographically sprawling country compared to South Africa.

In part, for both countries, out existing immunity defenses have largely failed.  Near as I can tell, neither prior infection (the main South African source of immunity to COVID) nor full vaccination (the main U.S. source of immunity to COVID) does much of anything against Omicron.  There, only the boostered population has significant resistance to symptomatic infection.  And that would argue for a smaller wave in the U.S. than in South Africa, as about 30% of our population has been boostered (against what I believe to be a negligible fraction of the South African population.)

Finally, in that case, if our main defenses against COVID-19 fail against Omicron, we’re down to our backups.  That’s mask wearing, distancing, and avoiding high-risk situations.  More-or-less, it’s as if we’re back to the start of the pandemic, and the only real barrier to transmission is COVID hygiene.

South Africa never took down its backup systems.  It had kept restrictions on some forms of social activity in place since the start of the pandemic.  It made mask-wearing outside the home a legal requirement, and enforced that.  And it kept that legal requirement in place, even after the end of the Delta wave.

In the U.S. by contrast, we dismantled the backups.  And that seems to be permanent.  The issue of mask-wearing has been so poisoned by the Republican party that few governors have the stomach for putting any sort of mask mandates back in place. (Or, alternatively, the U.S. population is so full of snowflakes on this issue that few governors dare to do that.)

And so, as a country, we’ve gone into the Omicron wave with no effective vaccine (without a booster shot), no effective protection based on prior infections, and a Republican-driven culture that prevents mere re-imposition of a mask mandate, let alone enforcement of it.

In effect, we have made ourselves purposefully defenseless.  No immunity, no mask.  Nothing except the booster shots, and the common sense of the people.

Once I boil it down that way, I guess it all starts to make sense.  We’ve already had far more cases that I would have remotely believed possible.  And it’s not clear that there’s a light at the end of the tunnel yet.

I keep asking “are we done being stupid yet”?  And the answer keeps coming back, “No”.  I got my prediction wrong.  But as a country, I think we’re fundamentally getting Omicron wave wrong.  If we have no effective immunity, and hospitals are starting to fill, we’re right back where we were in the winter of 2020.  And out COVID-19 hygiene ought to reflect that. But it doesn’t.

To sum up the U.S. situation:  We have

  • no immunity from prior infection,
  • no immunity from two-shot vaccination,
  • no mask use or other COVID hygiene policies,
  • no way to reimpose any such hygiene, and
  • a new variant that is off-the-charts contagious. 

In that context, an overwhelming U.S. Omicron wave starts to make sense.

Maybe things will turn out OK anyway.  Maybe we won’t generate enough cases to overwhelm the hospital system.  Maybe there will be a huge number of hospitalizations, but not so many ICU cases that hospitals run out of ICU beds.

Maybe we’re due for a break any day now.  But in the middle of what I’ve termed the “don’t give a damn” wave, we sure aren’t doing one whole heck of a lot to make that happen.

Post #1379: Omicron, the don’t-care wave of COVID-19

What is wrong with this picture?

Source:  Carnegie-Mellon University COVIDcast, accessed 1/1/2022

This post is more-or-less a followup on the just-prior post, where I found out that we’re now admitting as many people to the hospital under Omicron as we did at the peak of the Delta wave.  We’ve managed to offset the lower virulence of Omicron with a vastly higher number of cases.  And the peak of the Omicron wave is nowhere in sight.

And, near as I can tell, other than hospital workers, people just don’t seem to care.  Which I find odd and irrational.  But it is what it is.

And that’s the topic of this post.

Along with COVID in children.  For which, I will say up front, Omicron does not appear to disproportionately affect children.  In Virginia, there was no change in pediatric share of COVID-19 cases over the month of December.

Background:  The shifting situation

People tend to fuzzy-think their way through a lot of situations in life.   They get hold of an idea that sounds good, and they don’t bother to take a hard and objective look at it, as long as they are comfortable with it.

By now we’ve all heard that Omicron is less virulent than Delta.  And so, I guess we are each, individually, thinking that we’re in some sense a lot safer now with Omicron than we were with Delta.

Let’s call that a warm-and-fuzzy-thinking view of Omicron.  It’s not so bad, on a per-case basis.  Lot better than Delta, say, which had a reputation for virulent infections.

But those of us capable of doing simple math reach a different conclusion.  My likelihood of ending up in the hospital under Omicron is now just about exactly what it was at the peak of the Delta wave.  That’s because my odds depend on two factors:

  • Odds of hospitalization = odds of infection x odds of hospitalization, once infected.

For sure, the second term is lower under Omicron than Delta.  Maybe one-third as large.  But give it another couple of days, and the odds of infection term will have more than offset that.  The current situation is best described as:

  • Odds of hospitalization, Omicron = 3*Delta X (1/3)*Delta
  • Odds of hospitalization, Omicron = Odds of hospitalization, Delta.

Oh, and cases are now doubling roughly every week.  And two doses of vaccine does almost nothing to prevent Omicron infection.   And reinfections are common among those who have already recovered from some prior variant.

And nobody seems terribly concerned.

Doesn’t that strike you as odd?

And yet, nobody seems terribly concerned

Let me just start with my home town.  As documented in Post #1377, three days ago they were blithely going to shut down a drive-through COVID-19 testing center in town.  Which, as it turns out, would have reduced local testing capacity by about a third.  (Although I am almost sure they didn’t bother to figure that out first.)  Based on news reports, Town officials appeared absolutely unconcerned about the impact that might have.  Only after significant citizen protest did common sense prevail, and the Town bureaucracy agreed to allow the testing site to remain open another month.

In my state of Virginia, it looks like the Governor’s emergency orders all ended with the end of 2021.  The only mask requirements are that masks must be worn in schools and on public transportation.  (I’m pretty sure the second one is a Federal requirement).  There’s no talk of (e.g.) limiting occupancy of bars and other high-transmission-risk areas.

Schools?  Again, I’m seeing no talk of virtual schooling in my area, for grade schools.  My daughter’s college (and many others) are going to require a booster shot for return to campus, for those eligible, and will require mask use in commons areas.  So far, it doesn’t look like they will require a negative COVID-19 test prior to return to campus.

And, noted at the top of the post, about a third of people who were wearing masks last winter can’t be bothered to put them back on this winter.

In short, almost no COVID hygiene will be enforced, aside from masks in schools (in Virginia, anyway).    Private academic institutions seem to be moving to a standard of masks and booster shots.  Beyond that, a lot of people aren’t going to undertake that hygiene voluntarily, and it sure looks like, with a few exceptions, there isn’t a whole lot of lifestyle modification going on.

Against a background where new cases are doubling every week.

I wonder what’s going to happen when everybody goes back to school?

A quick look at pediatric COVID cases.

Let me start by reminding you of what happened when U.S. kids went back to school this past fall:  Nothing.  For sure, nothing happened in Virginia, because I tracked that pretty carefully (e.g., Post #1268).  And, I think that with a few exceptions in the upper Midwest, pretty much nothing happened anywhere.  There was some above-average spread among sports teams (a high-risk group due to close physical contact).  A few outbreaks.  And not much else.

I’ve never found a timely national data set showing new COVID-19 cases by age.  CDC will give you that information with a couple of weeks lag, based on their own case-reporting system.  But when cases are doubling every week, that might as well be a couple of years.

So I’m turning to data from Virginia.  We’re a middle-of-the-road state, we currently have 118 new COVID-19 cases / 100K / day, and the state Department of Health provides excellent, timely data, including a breakout of cases by age.  The data source is this file, updated to 12/30/2021.  If there’s been some big shift in COVID-19 cases, it should show up here.

There has been no change in pediatric share of cases under Omicron, in Virginia.  As Omicron has begun displacing Delta in Virginia, there has been no noticeable shift in the share of new COVID-19 cases that is for pediatric (under-age-18) cases.

Source:  Calculated from Virginia Department of Health data cited above, accessed on 1/1/2022.

Not quite tongue-in-cheek, I’ll also provide this information as a service to parents of Virginia school-age children who may be worried about the impending return-to-school.

Source:  Calculated from Virginia Department of Health data cited above, accessed on 1/1/2022.

There are about 1.7M persons under the age of 18 in Virginia.  There was one COVID-19 death in December.  Over the entire course of the pandemic, there have been 12 pediatric deaths attributed to COVID-19, for a risk of death, for persons under age 18, of about 0.0004% per year.

That said, this is is non-negligible risk of hospitalization.  Combining Federal and State data for December, the COVID-19 case hospitalization rate for the pediatric population of Virginia was just over 1 percent.  So while risk of death is vanishingly small, risk of being hospitalized with COVID is currently about one-in-100 diagnosed pediatric infections, in Virginia.

But what about rising pediatric hospitalizations under Omicron?

In the U.S., as was seen in South Africa and elsewhere, it looks like there’s a significant increase in hospital admissions for children with COVID-19.  I did the graph just a few days ago, for the U.S.:

Source:  Calculated from U.S. DHHS Patient Impact and Hospital Capacity by State Timeseries

(I would love to redo this now, for Virginia, but the pediatric admissions data are too sparse.  In a typical December 2021 day, pediatric (under age 18) admissions for COVID-19 were in the single digits.  The resulting pediatric fraction of cases is all over the map.)

My most plausible answer for the apparent increase in pediatric admissions for COVID-19 is that it may be due to persons admitted with, but not for, COVID-19.  I went through this distinction in Post #1351, principal versus secondary diagnosis of COVID-19.  And maybe that shows up disproportionately in the pediatric population because the COVID hospitalization rate is so low?

And yet, every time I try a back-of-the-envelope calculation, I’m not sure I can justify that.

But I will note, as a matter of fact and not speculation, that pediatric admissions rose as a fraction of total at the peak of the Delta wave as well:

So, at the very least, this isn’t the first time this has happened.  And the speed of increase in the pediatric share appears to correlated with the speed of increase of total cases in the population.

So I have to speculate that this “increased pediatric share of admissions” might be an artifact of the high prevalence of COVID-19 in the population.  That, somehow, those “stray” cases of people hospitalized “with-but-not-for” COVID disproportionately affect pediatric admission counts.

I just can’t find a way to prove it.  But at least now I can tell you that this happened in the last COVID-19 wave as well.

Let us all now collectively hold our breath as children everywhere return to school next week.  Given how fast Omicron moves, by mid-January we’ll know whether that’s a mistake or not.

Post #1378: COVID-19 trend to 12/31/2021, to infinity and beyond? No, just to the day after tomorrow.

For sure, this wouldn’t be my choice of ways to greet the new year.  But it is what it is.

We’re now two full weeks since the 12/17/2021 start of the Omicron wave in the U.S., and there’s still no letup in sight.  The U.S. daily new COVID-19 case rate doubled last week.  Continue reading Post #1378: COVID-19 trend to 12/31/2021, to infinity and beyond? No, just to the day after tomorrow.

Post #1377: COVID-19 and the Town of Vienna, VA

 

Edit:  The Town has since relented, which I believe is thanks to the efforts of Councilmembers Patel and Springsteen.  The testing center will remain open another month.  Which should get us past the peak of the Omicron wave.  Apparently, what was stated as flatly impossible two days ago turns out to have been a judgement call.  And reasonable judgement has prevailed.

Original post follows:

The facts are these.  There’s a drive-through COVID-19 testing site that operates in a church parking lot in the western part of Vienna, VA.  It has been operating since March 2021.  It appears to be one of the few drive-through testing sites in the nearby area.

Lately, as you might imagine with the rapid spread of Omicron, this site has been quite busy, with cars lining up to be served.  Reportedly, the operators of this site provide about 100 COVID-19 tests per day.  They offer both antigen (rapid) and PCR tests.

And now, as Omicron cases continue to ramp up, and access to testing becomes an increasingly important public health issue, the Town of Vienna is shutting down that drive-through testing station.  Today, last I heard. Continue reading Post #1377: COVID-19 and the Town of Vienna, VA

Post #1375: U.S. hospital bed and ICU bed use over the pandemic.

 

Source:  CDC COVID data tracker, accessed 12/30/2021

From time to time I’ve been tracking COVID-19 hospitalizations from a data file collected and maintained by the U.S. Department of Health and Human Services.  You can see a daily summary of the data by state, at this link.  DHHS also provides a weekly report showing individual hospitals, at this link.

In addition to counts of COVID-19 admissions and patients, that file also gathers some measures of how stressed the hospital system is.  For example, it captures the fraction of hospitals that report having a critical staffing shortage; it can be used to show the fraction of beds and staffed ICU beds currently occupied; and so on. Continue reading Post #1375: U.S. hospital bed and ICU bed use over the pandemic.

Post #1374: COVID-19 trend to 12/29/2021. I reject your reality and substitute my own.

 

This has been yet another morning of looking at the COVID-19 numbers and saying “never seen that before”.

In any case, I’m sure you won’t be able to avoid hearing all the bad news, so let me be brief about that.

The U.S. is now averaging more than 90 new COVID cases per 100,000 population per day.  Here’s how the case counts look, compared to last year: Continue reading Post #1374: COVID-19 trend to 12/29/2021. I reject your reality and substitute my own.

Post #1373: Omicron average case severity in the U.S.

 

The point of this post is to try to get some handle on the actual, as-observed average severity of Omicron, compared to Delta, in the U.S.A.  The bottom line is that the U.S. results look more like research from Scotland and England — the case hospitalization rate for Omicron is about one-third that of Delta.  They don’t look as good as the results from South Africa, which suggested that the case hospitalization rate was one-fifth that of Delta.

The same analysis verifies that there has been an uptick in pediatric hospital admissions with COVID-19, as a fraction of the total.  Not a huge increase, but a marked increase that coincides with the Omicron wave.  Given that we have no national database that shows current new cases broken out by age, there’s no way to tell whether that’s just an artifact of higher infection rates among the pediatric population.

Finally, I think it’s too soon to say much about U.S. mortality rates from Omicron compared to Delta.  The well-aged South African data seem to show a case mortality rate for Omicron that is about one-fifth that of Delta.  But data from European countries — which may or may not be well-aged enough to provide a valid estimate — show a much smaller difference.

All told, this means that Omicron is not quite as benign as the flu.  Best guess, with current data, case hospitalization rate is about twice that of flu, and my guess for a case mortality rate would be about four times that of typical seasonal flu in the U.S.

You can see my original comparison of Omicron and flu in Post #1364.  If our results had matched those of South Africa, then Omicron would have had a flu-like case hospitalization rate.  Now that it’s looking like our results aren’t that good, the best estimate is that Omicron has not-quite-double the case hospitalization rate of typical seasonal flu.

U.S. case hospitalization rate

Let me start with the case hospitalization rate.   That is, the fraction of newly diagnosed COVID-19 cases that are admitted to the hospital.

Below is the crude case hospitalization rate.  The plot is the seven-day moving average of new adult and pediatric admissions with confirmed COVID-19 at time of admission, divided by the seven-day moving average of new COVID-19 cases.

Source:  Calculated from U.S. DHHS unified hospitalization data set, and new case counts from the CDC COVID data tracker.

You can clearly see what appears to be the Omicron impact circled in red.  I date the Omicron wave to 12/17/2021.  Before that, the case hospitalization rate was about 6.5%.  As of the last day show, it has plummeted to 4.0%.  That fairly abrupt change certainly has all the earmarks of cause-and-effect, given the relatively stable rate prior to that point.

That’s the easy part.

The hard part is guessing what the Delta/Omicron mix is, corresponding to that 4% case hospitalization rate.  And here, I’m not going to get all fancy.  That’s a seven-day moving average ending 12/27.  So the median day is somewhere around 12/23 or 12/24.  Which is roughly contemporaneous with the last CDC estimate of Omicron’s share of cases (week ending 12/25).  So I’m just going to take the CDC’s number.  I’m just going to assume that 59% of those cases were Omicron.

The rest is just a bit of trial-and-error with Excel.

  • If the case hospitalization rate under Delta was 6.5%,
  • and the case hospitalization under a 31%/59% Delta/Omicron mix is 4%,
  • then the case hospitalization rate for Omicron must be 2.3%

To sum that up, it looks like Omicron’s case hospitalization rate is about one-third of Delta’s rate.  That’s in the ballpark of more careful estimates from Scotland and England.  But much higher than the South African estimate that Omicron had just one-fifth the case hospitalization rate.  Plausibly, that would depend, in part, on differences in propensity to hospitalize persons in those countries.

A little sensitivity analysis is called for.  By far, the most uncertain aspect of this is the fraction of newly-diagnoses cases that are Omicron.  The CDC didn’t actually say that Omicron accounted for 59% of cases.  The CDC actually said that there’s a 95% chance that Omicron accounted for between 42% and 74% of new cases.  Like so:

Source:  CDC COVID data tracker, accessed 12/29/2021.

We can use the range of the CDC’s confidence interval for the percent of  cases that are Omicron to show how this calculation of the estimated case hospitalization rate would change.  Same algebra as above, just a different set of assumptions.

I think the important lesson is from the bottom line of the table.  At worst — using the upper bound of the CDC’s confidence interval for its estimate of Omicron as a share of cases — the case hospitalization rate for Omicron is less than half that of Delta.

Some caveats.

Is it too soon to say anything meaningful about Omicron’s case hospitalization rate?  No.  I already dealt with the objection that hospitalizations lag new cases in prior posts.  There are plenty of real-life lags between (e.g.) date of infection, symptom onset, and hospitalization.  But as-reported, with all reporting lags included, the new cases and new hospitalizations series are very nearly exactly contemporaneous. The average lag between changes in reported new cases and changes in reported hospitalizations is one day.

Is this estimate going to mistake changes in vaccination rates and such with differences between Delta and Omicron?  No.  Because Omicron has grown so quickly, I can compare the U.S. today to the U.S. just a couple of weeks ago.  More-or-less the same population, more-or-less the same vaccination rate.   Not much changed in the past couple of weeks.

It’s possible that there may be significant demographic differences between the Omicron-infected and the Delta-infected.  But a) I doubt that, and b) there’s no timely data source in the U.S. that would tell us that.  So that remains a caveat.

Footnote:  Pediatric admissions as fraction of total.

There have been a lot of stories about increased pediatric admissions for COVID.  But, you know, anything having to do with dying children always gets a lot of press coverage.  So the question is, for the U.S. as a whole, is it true that pediatric admissions with COVID-19 have increased disproportionately?

The short answer is yes.   Below you see that pediatric admissions have gone from about 2.5% of admissions with COVID-19 to about 3.5%, over the course of the Omicron wave so far. As with the graph above, that short, sharp increase has all the earmarks of being cause-and-effect.

Source:  Calculated from U.S. DHHS unified hospital admission data. accessed 12/29/2021.

In terms of the absolute number of cases, this amounts to about 350 children per day admitted to the hospital with COVID.

There are two things to keep in mind.

First, we don’t know what fraction of those are admitted for treatment for COVID, versus admissions where the COVID is an incidental finding.  Near as I can tell, the U.S. data track something akin to “COVID present on admission”.  They are not tracking cases with COVID as the principal diagnosis (the reason for admission, see Post #1351).

Second, we don’t know what fraction of new cases are pediatric cases.  This might just be tracking the trend in new cases, for all we know.  There is no timely national data set that breaks out the new case counts by age.

Case mortality rate.

I can’t even hazard a good guess here.

In addition to the case hospitalization rate, I’d like to have some idea of the case mortality rate. What fraction of diagnosed Omicron cases go on to die from it?  In the U.S, for Delta, for the most recent period, that number has been just over 1 percent.

It’s too early to see Omicron’s impact on the U.S. case mortality rate.  There’s roughly a two week lag between reported new cases and reported deaths, and two weeks ago Omicron was barely on the horizon in the U.S.

Instead, I looked at three countries where Omicron hit earlier than it did in the U.S.  It’s not clear that any of these provides a good comparison.

In South Africa, the most recent data are all Omicron.  Between they had a material increase in vaccination rate between their prior (Delta) and current (Omicron) waves.  The apparent five-fold reduction in case mortality might be due, in part, to concentrating vaccinations among the highest-risk (e.g., elderly) population.

For two other countries where we can plausibly compare the mortality rates (Great Britain,  Norway), you really can’t see much of an impact of Omicron on the case mortality rate.  I don’t really know why.  I can only guess that this remains an artifact of the long time lags required to gather the mortality data.  In both cases, we’re looking at new cases that appeared in late November/early December.  Even with those countries, Omicron probably wasn’t a big enough factor to have generated large changes in the mortality rate yet.

At the end of the day, in the U.S., all I can do is take a guess.

I’m going to guess that we’ll see about the same effect on case mortality as we see on case hospitalization.   Probably, the ultimate case mortality rate for Omicron is going to end up being somewhere around a third that of Delta.   (I say that mostly because that’s how the Virginia numbers look, for vaccinated versus unvaccinated persons, under Delta.  The reduction in the mortality rate due to vaccination is always similar to the reduction in the hospitalization rate.)

If so, that will make Omicron considerably deadlier than seasonal flu.  A one-third reduction relative to Delta would result in a roughly 0.4% case mortality rate for Delta in the U.S., compared to a 0.1% case mortality rate for flu in the U.S.

My conclusion is much the same as for hospitalizations.  Omicron appears much less virulent than Delta.  But it’s an exaggeration to say that it’s no worse than flu.  Best guess, given what I can get my hands on today, it’ll result in about twice the hospitalization rate and four times the death rate of flu.

(And, of course, those who claim COVID is no worse than “a cold” are just ill-informed.  First, “a cold” is not a single well-defined disease, but refers to the symptoms of any number of upper respiratory viral infections.  Second, near as I can tell, you can’t even find a case mortality estimate for “a cold”, presumably because deaths attributable to complications of a cold are so rare.  Third, the same goes for a case hospitalization rate for “a cold”.  People who claim COVID is no worse than a cold have probably never even tried to look up the actual case hospitalization and mortality data.)

In short, if you’re in one of the higher-risk populations, I think it’s still well worth your while to avoid this strain of COVID.  It’s as prevalent in the population now as it was at the peak of last year’s winter wave.  And while your odds of hospitalization and death, if infected, are lower now than they were then, they are still non-negligible.  Best guess, as of today, if you get infected, you’ve got a better than 1-in-50 chance of ending up in the hospital.