The curve & Farr’s Law
In the mid-19th century, Dr. William Farr, observed that epidemic events rise and fall in a roughly symmetrical pattern that can be approximated by a bell-shaped curve. He noticed that this time-evolution behavior could be captured by a single mathematical formula (“Farr’s law”) that could be used for epidemic forecasting.
Our curves look like that what Farr’s law predicts:
All Cause Deaths for the NJ Department of Health
NJ Deaths from theNew York Times
We are close to Herd Immunity in NJ
The CDC has establish the most likely COVID-19 death rate to be 0.0026 or 0.26%. There have been 13,355 (NJ DoH) to 15,211(Johns Hopkins University) deaths in NJ out of a total population of 8,882,000. Basic algebra allows us to roughly back calculate (credit to JB Handley for the explanation) the total number of infections in NJ based on the total number of deaths and total population. This is very crude math but it may give us a hint to part of what is going on in NJ.
This gives us a total number of infections in NJ in the range of 5,137,538 to 5,759,615 which puts us at 57.8% to 65% of NJ infected. Not quite the 70% needed for herd immunity, but pretty close. So something else might be going on here.
Just to drive this point home, here is a graph created by Hold2 showing the results of the same calculations for the whole USA. This method is far more accurate than testing. The red curve is deaths, lagging about 14 days behind the actual infections in the country. As you can see, the detected cases (in blue) are just the tip of the iceberg.
Brain Scientist Hints at Something Else
Neuroscientist Karl Friston, of University College London, builds mathematical models of human brain function and has applied his generative models to COVID-19 with some success. More importantly his “models support the idea that what happens in the next few weeks is not going to have a great impact in terms of triggering a rebound – because the population is protected to some extent by immunity acquired during the first wave.”
Dr. Friston explains the models are hinting at some immunological “dark matter” that results in “people who are impervious to infection, perhaps because they are geographically isolated or have some kind of natural resistance.”
As it turns out, current research is pointing to T cells as the potential immunological “dark matter.”
T-Cells may be more important than anti-bodies
There is mounting evidence that T-cells are essential to fighting SARS-CoV-2 and studies reveal infected people harbor T-cells that target the virus. Studies have also found people never infected with SARS-CoV-2 have these T-cell defenses, most likely because they were previously infected with other coronaviruses, like the common cold. The percentage of individuals with T-cell protection vary in each study as Braun et al. (2020) found 32%, Grifoni et al. (2020)found 40 – 60%, and Nelde et al. (2020) found 81%.
These results suggest the “dark matter” Dr. Friston is seeing in his models are T-cells that allow a large portion of the population to deal with the virus due to a small residual immunity from our exposure to common cold viruses.
Even if only 30% of people in NJ have this T-cell protection, it would likely push us over the herd immunity threshold, ending the COVID-19 pandemic for us.
I’ll leave you with this graph from The Ethical Skeptic on Twitter who nailed the IFR weeks before the CDC. Here he shows how the CDC All Cause Fatalities has dipped below the 2014 – 2017 average indicating the pandemic might be over for the United States as a whole.