Coronavirus Newsletter -- Herd Immunity

General Update / Herd Immunity: What Is It? / Achieving It / 20% Theory / An Alternative / What Comes Next?

The good news is that new cases are down, deaths are slightly down, and with recoveries increasing, active cases may be going down soon. It's enough to tempt some to think this thing is finally ending, but not so fast ... there's actually much more opportunity for this virus to spread -- as you'll learn about shortly.

Today we'll be talking about herd immunity -- what is it? How close are we? How, if ever, will this pandemic end? But first ...

General Update
The hotspot map for the US is lightening up overall, though a few places are still showing high activity: east Georgia, west Tennessee, northern Florida, east Texas, northern Mississippi, eastern Oklahoma, splotches all up and down the mid-west, highway corridors of Idaho and Washington, and central California.

Louisiana is looking much better, and maybe Alabama as well.

I'm sad to report that South Korea has had a resurgence, mainly due to a large non-compliant church in Seoul -- I may talk about this next week -- I'm still thinking about what next week's topic will be. I have full confidence that Korea will get on top of this and get back to being awesome.

Spain is having a major resurgence, which may be similar to our mini-second wave. Japan has had a second wave that makes the first wave look like little stuffs ... and deaths have already started picking up.

Brazil at its current rate is likely to surpass the US in total death counts in the next month or so, and then Mexico and India may be next to surpass the US.

But enough of this diddling ... let's get on to herd immunity.

Herd Immunity: What Is It?
This term -- herd immunity -- has been floating around the news for months now. Most of the time, it seems that people don't really understand what it is or what it means.

In a nutshell, herd immunity is supposed to describe a situation in which so many people become immune that the virus has a harder time finding people to infect and starts to die out.

More technically, herd immunity is when the current reproductive number falls below 1.0 under normal circumstances (no lockdowns, no restrictions, economy fully open, etc.). Or another words, active cases start dropping on their own.

Check this picture out from worldometers.com, as it will help to understand the terminology.

This shows currently active cases for the United States. You can see our first wave from March to May, and then as recoveries started kicking in and new cases dropped, active cases went down for a few days. I remember being excited about it, but then the second wave started. Now near the end of August, it looks like we're at another turning point. Maybe it'll start going down this next week. Eventually, we could get it all the way back down to zero.

The end of June, and the end of August (I hope) are what I'll call moments of artificial herd immunity. What this means is, we, as a society took artificial measures to slow down the spread of the virus. The first immunity in June came from nearly-nationwide lockdowns through mid-May, which successfully brought down daily new cases to lower levels. The second immunity that might come next week is likely a combination of continual self-distancing, warmer weather, and wearing masks more consistently.

But this isn't a "true" herd immunity, as that can only be measured when there are no artificial measures being taken ... that is, no masks, no distancing, etc. In other words, if we were to do away with our current artificial measures, cases would likely continue increasing until we hit "true" herd immunity.

And even then, it's nearly impossible to pin down "true" herd immunity because of a wide variety of factors. You may have heard that we need at least 60% infected to achieve this immunity, but in some areas where population density is lower, it could happen at 40%. In more dense areas like New York City, it would probably happen more like at 80%.

Weather can also play a role. There appears to be evidence that hot weather does indeed slow down the virus, so herd immunity can happen sooner. But as soon as cold weather hits, a higher threshold might be needed.

So, pinning down the exact immunity percentage needed for herd immunity can rely on an ever-changing set of complex variables.

BTW, You're probably wondering how experts estimate the herd immunity percentage. Well, have no fear, I'm about to reveal all.

It all comes from the SIR model. To understand this model, I've found no better video than this one I've shared before on my Facebook page:




In this video, herd immunity is represented in the "do nothing" scenario when the orange Infectious curve starts to go down. The initial Reproductive number, usually called R0 (R-naught), represents the speed of infection at the very beginning of an epidemic. Some people think of this as an average number of people one person may infect over a certain amount of time. As the disease increases, the Reproductive number will drop as more and more people become immune. This is usually called Rt (R at time 't'). And herd immunity happens when Rt falls under 1.0. You can think about it in this way ... if Rt = 0.9, then one person is infecting less than one person -- in other words, the virus is going to die out -- if I infect 0.9 people, they're going to infect 0.81 people, who will then infect 0.729 people, and so on until it dies out.

And after running all these SIR models, and even comparing with actual epidemics, epidemiologists have come up with a nice formula. If you can measure R0 at the very beginning, then the needed herd immunity threshold happens at 1 - (1/R0).

Example: Measles has an estimated R0 of 12-18, which provides an estimate of herd immunity at 92% - 94%.

For COVID-19, R0 is estimated to be from 2-6, which translates to herd immunity at 50% - 83%.

The Spanish Flu was estimated to be from 1.4 - 2.8, with herd immunity from 29% - 64%.

You can get all the boring details of R0 and the herd immunity formula in this wiki article.

Before moving on, I need to clear up one more misconception. Some people seem to think that when we get to herd immunity, people will stop getting sick, but that's clearly not the case. In my 0.9 example above, the 0.9 people I infected in turn infected more and more people until a total of 10 are infected before it dies out.

Or think of it this way -- if I haven't yet gotten the virus, and we've hit herd immunity, and if I lock myself in a room with an infected person, do I somehow become magically protected? I hope you answer no and realize that people will continue to die even when we hit herd immunity.

Herd Immunity: Achieving It
So how do we get there?

The easiest way is to just do nothing ... open everything up, and let the virus run its course. This is indeed an option -- in fact, many have suggested it. The UK tried this approach from the beginning before resorting to lockdowns, and as a result has one of the highest deaths per million in the world. Sweden also kind-of tried a version of herd immunity, which also led to similarly high deaths per capita.

The idea is that if it happens quickly (but yet slow enough to where our hospitals can handle the demand), then we can get it over with and then watch the virus die out in the end.

Another variant is to introduce vaccines -- to help people become immune. Say we need 70% for herd immunity. If 20% have already caught the virus and 50% get effectively immunized, then that would bring us up to 70% -- it doesn't matter how people become immune -- it just needs to get up to the threshold.

We've already tried artificial means to obtain a lower artificial herd immunity, but if the artificial means are relaxed too early, then the virus begins spreading like before. These artificial means include lockdowns, wearing masks, washing hands more than usual, quarantining the sick and exposed (which requires effective contact tracing and testing).

Herd Immunity: 20% Theory
Before on my Facebook page, I shared a popular theory that's been going around ... that herd immunity for COVID-19 may be closer to 20%. Here's a good summary of that idea:

https://theconversation.com/coronavirus-could-it-be-burning-out-after-20-of-a-population-is-infected-141584?fbclid=IwAR39_cLMtgb0rr4VOUpy_0tzJWPPkpeO0za_bS5h7qYnQ21h0cFJi3ym6bc

In several instances throughout the world, it's been observed that, according to antibody studies, only 20% of the people got infected, and then the virus disappeared. This has apparently happened in New York, Stockholm, London, and even on the Diamond Princess.

And look at Sweden right now ... they've probably hit about 20% exposure, and for some reason, it has suddenly died out. Could there be truth in this theory?

The idea is that most of us already have T-cell immunity from exposure to the earlier much-less dangerous coronavirus that causes a version of the common cold. That is, many of us probably already have T-cells that recognize the protein surfaces of this new coronavirus, because they are similar to most other coronaviruses.

I do think T-cells will ultimately prove to be key in helping to create a type of vaccine or protection once we figure it out, but after thinking about this more, I think the 20% theory is wrong, and here's why ...

• I think we're seeing examples of artificial herd immunity. 
• In Sweden, many people are self-distancing, which is artificially lowering the threshold. Also, lower population density is probably going to require a lower true threshold.
• In some areas, antibody tests have revealed much higher exposures.
• Some sections of NYC have shown exposures as high as 80%-90%. Perhaps higher density destroys the 20% theory? Or these sections of NYC were somehow unexposed to earlier coronaviruses?
• I believe heat in some areas is contributing to a temporarily low immunity threshold.
• And ... if T-Cells really are providing complete immunity (that is -- they don't even test positive for this virus or related antibodies), then it would have shown up in early calculations of R0. 20% herd immunity corresponds to an R0 = 1.25.
• Then again, this virus is exhibiting a super-spreader pattern rather than a smooth spread pattern, which could by itself change the rules and make the SIR model less applicable.
• And finally ... don't look now, but Sweden and a lot of other countries are starting to see resurgences. In a couple of months, I think we'll see that 20% is wrong.

Herd Immunity: An Alternative
I actually hate the idea of obtaining herd immunity, because I think the cost would be too high. The mortality rate for this virus is estimated to be in the 0.5%-1.0% range. If the entire population of the US were to catch this virus, that would be 330 million cases, which would then result in 1.65-3.30 million cases. If herd immunity causes only 270 million to be exposed before disappearing entirely, that would still be 1.35-2.70 million deaths. And right now we're just at 0.18 million deaths.

Also, if we let this get to herd immunity, it greatly increases the chances of it never ever going away. Just like the Spanish Flu, which has since mutated into other H1N1 strains, though we are much more capable of treating its symptoms and have really cut down on deaths.

The only other real alternative is eradication, which is basically obtaining a really low artificially herd immunity through artificial means for an extended amount of time until the virus dies out.

Other countries have shown that this is more than possible. China has practically eradicated several outbreaks. The US eradicated Ebola on our soil around 2014. With COVID-19, several countries had eradicated it, or gotten close: New Zealand, South Korea, Japan, China. Some of these countries have achieved this even without locking down. Though, it's also been shown to be difficult to maintain when other countries are doing a terrible job eradicating and reinfecting them.

Wearing masks, social distancing, effective contact tracing, taking on personal responsibility, and so on, have proven to be effective -- not only in fighting COVID-19, but also other recent outbreaks. If you watched that cool video above, then you've probably already seen that the "quarantine sick and exposed" scenario was the most effective way to fight the virus.

To me, it seems like the much preferred option. I think we could achieve it even now with smart strategies and safety precautions that would relatively quickly kill off the virus -- even before a vaccine is created.

What Comes Next?
So what do we do next? It's entirely up to us. If the entire world were to incorporate smart strategies at the same time, this virus would be gone in a matter of weeks -- not months. And then we could go right back to normal.

The only other option is to let the virus win and take us to full herd immunity -- and that only comes at a high price.