These are my thoughts on Covid-19, since about mid to late March. They might be wrong. So far, there has been growing evidence for key pieces of this story.
Here’s the story:
This represents total Covid-19 infections in the population. It started much earlier than we think. I’m guessing December, but I wouldn’t be surprised if it was earlier.
I think infections tend to grow to 5-10% of the population and then continue to roll through at about that same rate, driving a fairly consistent case load.
This is the weakest part of my story. I haven’t thought of a good reason why it grows to 5-10% of the population fairly quickly and then levels off. Some reasons might be that infected folks and those around them start taking basic precautions like staying home from work, washing their hands when they’re around sick folks or avoiding them altogether.
But, my observation is that’s similar to how other viruses seem to spread, roll through the population in waves, rather than exponentially. Of course, I’m no epidemiologist, so you can hurl that criticism. I’m just going off previous observations of how I see cold wave through.
This also means that the virus was likely far less deadly than we thought by just looking at tested cases, by a factor of 10 or more.
Evidence to support:
- Folks who died in January and maybe December did, indeed, are now being tested and shown to have had Covid-19.
- Antibody tests have been consistently supporting that actual number of cases is far greater (15-80x) higher than testing has identified and that many folks have such mild symptoms that they don’t think of getting tested.
- H1N1 was also originally thought to be 10-20x more deadly than it turned out to be, based on the fact that early testing didn’t identify every single case. As better estimates of full infection became known, fatality rates dropped to the top-end of flu ranges.
We came along a few months after the virus had already steady-stated and started ramping up testing quickly. There seemed to be the belief that the testing was uncovering the virus as it spread.
I believed that testing was just uncovering infections that were already near steady state in 5-10% of the population at the time of testing.
Think of it like testing to find people who are 6′-4″ or taller. The first day we test 100 folks and find 10 are tall. The second day we test 1,000 folks and find 100 are tall.
Would we conclude that tallness is spreading exponentially? No. We would understand that folks were tall before they were tested, the testing just identified the percent of the population that was tall.
Now, I realize this isn’t apples-to-apples, because viruses do spread, whereas tallness does not (at least not like viruses).
But, the point is that if the infections were present in 5-10% of the population, while testing was growing exponentially, it would be easy to conclude that the virus was spreading exponentially, when it really wasn’t.
Evidence to support:
- Growth in positive tests mirrored the growth in tests. See this post.
- Consistent positivity rate of covid-19 tests (also see that post).
After the first week, the testing positivity settled to about 20% for the next month, before dropping as test criteria started getting looser. It was 20%, because tests were only given to folks who thought they might have. So, the 20% would be a high estimate for percentage of total population that doesn’t have it.
So, this would be like if we just gave the tallness test to folks who felt they were pretty tall.
This led me to believe the 20% of the population was the way top-end estimate of percent of population infected at any one time. I guessed the actual rate of infection might be in the 5-10% range (although wouldn’t be surprised if the range was more like 3-15% just depending on local spread factors, like average number of folks in a household, mass transit, weather, etc.).
The blue-line represents the positive tests. I felt the number of identified cases were likely a fraction of the actual infections (red-line).
It grew with testing — freaking people out. But, leveled off when testing leveled off. Which was somewhat comforting to me. That supported that the virus was more of a steady-stater than an exponential grower.
What about the surge?
A fair question is why did we see a surge in cases in early April? As we are finding out, the most likely way to contract the virus is with close contact and many infections spread within homes.
It wasn’t lost on me that surges in positive tests, hospitalizations and deaths happen to occur 2-3 weeks following stay-at-home orders. I wasn’t the originator of this theory, but thought it had some potential when I first saw it.
I would not find it surprising that the surge was, at least partially, caused by a lot of folks putting themselves in the most highly transmissible environment (home) at about the same time.
I also think another contributor to the surge was hysteria drove infected folks (many who would normally have just gone about their business and recovered in a few days) into hospitals without the hospitals yet having good protocols to reduce the chance of transmission to the folks already in the hospital.
I wrote about on April 15.
If this is true, this is what I would expect to happen from here…
Cases and deaths will remain steady for some time as the virus works its way through the population.
In places like NYC, it seems like the virus is somewhere between 20 and 30% through the population already, which means we can expect 3-5x the number of cases and deaths to occur at some point in the future. But, it could be less if the virus has a hard time sustaining itself as more folks can fight it off.
In other places in the country, it may still be more like 10-15%.
Nobody knows what the top-end number needs to get to for herd immunity. I’ve read that it ranges from virus to virus from 60-90%, but even that is a fair amount of intelligent guessing from experts.
It makes sense to me that we start to see significant slowing after about 30% of the population, because that has essentially cut your chances of spreading it others randomly by 30%. At 50%, it cuts it in half.
What about future strains and waves?
I expect both will happen, but I don’t know if it will be as rough as the first go around. Simply because as more immune systems see this type of virus, they may have better chances of fighting off future strains.
But, I could totally be wrong.