Thread by @kylamb8

Herd Immunity. I'm devoting this thread to it because it's a possible way out. There are a lot of Herd Immunity Threshold (HIT) deniers out there over theories that the virus is burning out at 15-20%. I'm about to throw some cold water in the faces of the deniers.

1/2

I can't prove, and won't attempt to suggest I can, that we are reaching herd immunity in the U.S. However, after seeing the data I have to offer, anyone would be cray to dismiss the possibility out of hand. First, let's discuss what herd immunity actually is.

2/3

Let's explain herd immunity from an excerpt found on the Mayo Clinic website:

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mayoclinic.org/diseases-condi…

Generally speaking, herd immunity is reached when anywhere from 40 to 80 percent of a population has been infected. As mentioned by Mayo, measles needs 94% threshold before achieving immunity.

4/5

In the early days, when U.S. deaths projections were 2, 3 or 4 million people, it's because herd immunity was not considered reasonable to achieve without great loss of life. See this excerpt from MIT Technology Review on March 17.

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technologyreview.com/2020/03/17/905…

We have learned and are still learning a lot about this virus. It turns out, we might not need to get to 60 or 80% to achieve immunity. One possible explanation is T cell resistance.

See this July 28 entry on the NIH director's blog

6/7

directorsblog.nih.gov/2020/07/28/imm…

There is still a lot of pushback against T cell immunity, or at least whether it's possible it's providing a possible 15 to 20 percent immunity threshold.

Many people have now theorized the 15-20% burnout on observation and it was first popularized by @MLevitt_NP2013

7/8

I'm here to tell you, there is evidence for it. Getting data from covid19-projections.com which estimates the number of true infections (actual number with the virus rather than just confirmed cases), I found 15 states have reached at least 10% infected 45 days ago or more

8/9

First, let's look at 13 of those 15 states and see what 7 day case averages look like when done on a per 1 million basis (MS had unreliable case data and NY began so early in testing so both of these states were excluded); 21 days prior to reaching 10% threshold...

9/10

The previous chart shows a very similar upward trajectory in every state except for Louisiana, which was a clear outlier. Rhode Island was also a bit of an outlier, but most states continued to increase.

Now watch what happens when they hit 10 percent.

10/11

Although not every state was the exact same (Louisiana was an outlier again skyrocketing then sharply falling after 40+ days), states all level off and start falling within 1-3 weeks of hitting 10 percent. This fits the 15-20% threshold.

See the before & after.

11/12

Again, this is not proof of herd immunity threshold being 15-20% for Covid-19, but it's difficult to argue other causes. Mask mandates, lockdowns, etc. simply were not uniform. I have been on the fence on H.I.T., but this, for me, is strong evidence for it.

/End

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