COVID Archives

Why does COVID peak at such a low percentage of the population?

I’ve talked a lot over the past weeks about how COVID known active cases tend to peak in the range of 0.25% to 0.50% of the population in a given area, then decline. For the longest time it has puzzled me. However, I’ve been seeing more and more theories about full or partial immunity in a large swath of the population. Although I know little about medicine, this is quite congruent with the data, so I tend to believe it has some validity. Here is an article published today on CNN by Dr. Sanjay Gupta, postulating that as much as 50% of the population carries some level of built in resistance to COVID:

This may be the missing piece of the puzzle. I’m seeing a ceiling in known active cases of, let’s say 1/3 of one percent. Now bear with me for a little arithmetic — When a location reaches this threshold, roughly 5 times the active case count has confirmed positive, so that means something over 1.5% of the population has been confirmed to have had COVID. However, we know that the actual prevalence of the disease is a large multiple of known cases. There is quite a range here based on the various antibody studies, but the average consensus seems to be about 10x. Assuming that, when a locality reaches the ceiling, perhaps 15% of the population has had COVID in total. If we add this 15% to the 50% of the population that has some level of innate immunity, we have 65%, which is right in the range of herd immunity.

It’s puzzled me for quite some time why so few people contract this disease. Even with a prevalence multiplier of 10x, we’re just now (after 5 months) seeing numbers of cases that match the flu each year. If it’s so contagious (I also remain skeptical about that), and it doesn’t attenuate in the summer, why so few cases? I know there are a lot of assumptions in my arithmetic exercise above, but it’s the only theory that matches the data so far, so I’m inclined to believe it until we have a better explanation.

As always, feel free to send me your questions about my assumptions, methodology, or modeling in general.

  • Likely date of active case peak (Chalke modeling): July 23
  • Likely date of peak deaths (IHME): April 16 (last revision on July 30)
  • Total Test Results reported today: 725,902 (very high)
  • Total Pending tests reported today: 3,888 (extremely low)
  • National reported case Growth Rate today: 1.06% (very low)

Shane Chalke Interviews


Groom Ventures has agreed to host a website that will archive my daily reports, and supplement with other commentary. John Groom worked at one of my companies back in the day, and is an excellent writer. The website is: For those of you that post my daily report on Facebook, let me suggest you link to this site, as the direct Facebook posts don’t seem to copy the graphs.

Daily Analysis

This second wave of case growth, which began over 6 weeks ago, seems to have peaked about 10 days ago, and is in solid decline. Here is what it looks like today:

Every one of the 6 hot spots from the beginning of July is level or in decline.

Look at the daily new cases. We’re looking at a pattern of decline for about 2 ½ weeks now. The growth rate in cumulative cases has also declined – we hit just 1.06% today, a rate we haven’t seen since June 15th.

All the news now is about the daily death count, so let’s take a look at that. Here are the daily national deaths:

Deaths have risen from roughly 500 per day at the end of June to something over 1,000 a day over the past week. Some of this is reclassification of deaths ( but not much of can be explained this way. We are seeing a rise in daily deaths for about 3 weeks now. I believe it will attenuate soon, as the active case count is falling pretty fast. To help make sense of the daily death count, I’m going to continue to report my new statistic – daily deaths per 1,000 known active cases. Here it is.

It is obvious that this wave of COVID is far less deadly in relation to active case count. It also looks to be fairly stable, at just over 2 deaths per thousand active cases. We are in a much better situation than we were in April.

On to the states.

As I mentioned last week, Arizona is starting to look a lot like NY or MA, with a hard bounce off the population ceiling and a rapid decline from the peak. This state is down an amazing 36% from the peak of less than four weeks ago.

SC is now 16 days past peak. SC Peaked at 0.26% of the population, so I suspect this peak will hold. Note that South Carolina double counts cases, as they treat each positive test as a new case (per The Covid Tracking Project).

Here is Florida – 16 days past peak active cases. Interestingly, I noticed Miami flattening first, but Miami remains flat – it hasn’t declined yet at all, differing from the state as a whole. Florida peaked high, at 0.38% of the population, so I think this peak will hold. Florida is now down 24% from the top.

California continues to look better and better. If California peaked, it was 8 days ago. California’s peak was only at 0.18% of the population, so I keep thinking there is more to come, but let’s hope not. As always, I need to report that California is one of the states that counts tests rather than people.

Georgia is now flat for 15 days. Is this the top for Georgia? I don’t know. Georgia hit a high of 0.25% of the population, so this could be the ceiling – just below the average for states that have peaked. Note here again, the case numbers are exaggerated. Georgia counts each positive test as a case (according to The COVID Tracking Project).

Texas is making good progress. IF Texas peaked, it was 10 days ago at 0.23% of the population. I don’t know if this will hold, but it’s looking promising, down 29% from the top – looking like another Massachusetts. Texas also reports positive tests as cases, so is doing some level of double counting.

NC is looking pretty good for two weeks now, but if this is the peak, it’s at a very low level (0.14%). We’re scheduled to remain in Phase 2 until August 7th, but I’m thinking the case and death numbers are such that we “could” move to Phase 3 then. IHME is projecting peak daily deaths in NC now around August 10th. It’s interesting how NC and VA now move together since mid-June.

Here is the daily death report for NC. We’re seeing a mild upward slope in daily deaths, but I think this will reverse in the next 2 weeks, as known active cases are declining.

Washington could have peaked, but I’m skeptical, as the high water mark you see here is at just 0.087% of the population. It’s been 14 days, though, so this is hopeful.

Nothing to say about NY and NJ – the picture says it all. Interesting that NJ is drifting upward lately, which NY continues to gradually fall. I don’t know what to make of this, but both numbers are small in relation to where they’ve been.

The rise in Massachusetts over the past 4 days is a result of the discovery of new historical cases ( Massachusetts, to their credit, has been carefully working to place the new cases on the appropriate historical dates, but the aggregation sites pick them up as new cases, as I’m showing here. It doesn’t mean growth – just the opposite.

…And here is Michigan. Looking beautiful until June 10th, then beginning a steady upward drift. Michigan peaked at a low percentage of population (0.089%), so may continue to grow if my theory is correct. It is just one of several states that peaked early and low, and doesn’t seem to be done with COVID yet. Nonetheless, we see a big drop today.

PA has seen a 3 day decline. Encouraging, but I believe PA has more growth to come, as the peak was very low (0.091% of the population).

And finally, here is Colorado. Colorado is one of the states that has had aberrations in their data. I still report it, but I’ve shied away from any conclusions in this state due to the data irregularities. Very small numbers here. Colorado peaked at a very small percentage, so could peak again as well.

So that’s it for today. I’ll report again on Thursday.

The numbers are still very small as a percentage of the population. Unless you’re in a high density area, your chances of contracting COVID are very small. However, even though the probability is very small, that doesn’t help if you’re the one catching it. Everyone please continue to be as cautious as you feel necessary.

–Shane Chalke, FSA

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