So you think we should try herd immunity?

“Those whom the gods wish to destroy, they first make mad.”

- Ancient Greek saying, wrongly attributed by some to Aeschylus

It seems to be in the wind: Lots of people (on different ends of the political spectrum) are beginning to say things like “This lockdown stuff isn’t working, because people just don’t want to do it. Let’s just fully reopen the economy and wait for herd immunity to kick in. At that point we’ll have beaten the virus.” (although I would call this “surrendering to the virus”, not beating it)

What are the problems with this idea? Let me count them:

1. From the initial reactions to opening up in Georgia and Texas, it looks like it will be a hard sell getting most smaller businesses to reopen at all, and larger ones don’t want any part of the idea at the moment (except for the meat packers, of course. I notice a couple governors in agricultural states are making clear to the workers that, if the plant opens up and they don’t go back to work, they’ll lose their unemployment benefits. And by the way, be sure to vote for me in November! If you’re still alive, that is). The economy can’t recover until the virus is beaten, meaning new infections are rapidly declining, if not stopped altogether.
2. Unless a vaccine magically drops from the sky in a month or two, the only way we’ll get to herd immunity is if around two thirds of the US population becomes infected. Of course, a large number of those will be asymptomatic, but they will still be spreading the virus, and lots of the people they spread it to will have symptoms – and some will die, of course (think of a nursing home worker who is asymptomatic but has the virus. Unfortunately, it’s scenarios like this that have made nursing homes the biggest clusters of deaths).
3. Two thirds of the US population means about 215 million people will become infected before we reach herd immunity. How many of these will die? In South Korea (which has the virus very much under control, although they have to be constantly vigilant and react very quickly to any new cases), the case mortality rate appears to be about 1.5 percent so far. If we’re so lucky that our case mortality rate is somewhere close to that figure, it means we’ll have over 3 million deaths. I should really stop here, since going on means I think some people will find 3 million deaths to be acceptable (I don’t, but maybe I’m just an ultra-sensitive person. This is about equal to the population of the city of Chicago – next door to where I live. It’s a little hard for me to imagine all those people suddenly disappearing). I hope nobody does, but let’s continue anyway.
4. The whole idea of herd immunity assumes that, when someone becomes sick, they will be immune for a long time (hopefully the rest of their life, but at least a few years). SARS, which is also a coronavirus, has an average immunity period of no more than three years. That isn’t great, but this would certainly be acceptable if that’s what it is for the novel coronavirus. However, since the coronavirus has only been around 4-5 months, scientists can’t say anything definite about immunity. For all we know, it might be three months or even less. South Korean researchers said a couple weeks ago that they had identified 160 people who had previously either had Covid-19 or were tested positive for the coronavirus – but later tested negative, who had become re-infected. Of course, it’s possible the virus never went away, but was simply hiding in the intestines, where the test wouldn’t find it.
5. So if we’re going to gamble on herd immunity at this point, we’ll be taking the chance that 66% of our population will be infected (with 3+ million deaths), and all we’ve achieved is a month or two of protection before the next outbreak. This sure sounds like a great bet to me!
6. But even if herd immunity is reached and it does last say 2-3 years, the outbreak won’t be over then. The remaining 33% or so of the population can still become infected, since asymptomatic  infected people will still be walking around. It’s just that, with about 2/3 of the population protected, the spread will no longer be exponential (i.e. one infected person will infect more than one other person). Sooner or later, almost the whole population will be infected – it will just take longer to do that then it would have without herd immunity.
7. As a good article in the Times pointed out a couple days ago, the herd immunity concept really applies to the case where there’s a readily-available vaccine. When 2/3 of the population has been vaccinated and if the remaining people who are infected are quarantined, it will be very hard for the disease to spread much further. But when we reach the 2/3 point for Covid-19 infections and assuming there’s still no vaccine at that point, there will still be a lot of asymptomatic infected people walking around. They’ll still have plenty of people to infect, thank you.

And there’s something else hanging over all of this: I used a 1.5% case mortality rate to come up with the 3 million deaths estimate above. But we don’t have to guess at the rate: Since late March, we’ve known the ratio of deaths to closed cases in the US, with closed cases being equal to deaths plus recoveries. What does that ratio stand at today? I’ll save you the trouble of looking down below: It’s 28%. If I use that figure rather than 1.5%, this means that 60 million will die on our way to herd immunity. So if you think 3 million is unacceptable, you’ll presumably think 60 million is a lot worse than that. At least I hope you would.

The numbers

Since the projected numbers in the table aren’t changing that much recently and since it takes some time to update the table, I decided I will only do the projections every two or three days (they would have been down from yesterday, since the 3-day growth rate in deaths went down yesterday). I’ll always show the actual numbers, though.

I. Total deaths

Total US deaths as of yesterday: 67,448

Increase in deaths since previous day: 1,666 (vs. 1,911 yesterday)

Percent increase in deaths since previous day: 3% (vs. 3% yesterday)

Yesterday’s 3-day rate of increase in total deaths: 9% (This number is used to project deaths in the table above. It was 11% yesterday)

II. Total reported cases

I no longer pay any attention to the reported case number. It is a huge underestimate of actual cases, which is probably 25-50 times reported. This is because of the huge shortage of testing capacity. If reported cases were to be anywhere near actual cases, we would need to be doing 20-30 million tests a week. I believe the US has done about 6 million tests since the start of the pandemic.

Total US reported cases: 1,161,109

Increase in reported cases since previous day: 29,253

Percent increase in reported cases since yesterday: 3%

Percent increase in reported cases since 3 days previous: 9%

III. Reported case mortality rate so far in the pandemic in the US:

Total Recoveries in US as of yesterday: 173,725

Total Deaths as of yesterday: 67,448

Deaths so far as percentage of closed cases (=deaths + recoveries): 28% (vs. 29% yesterday) Let’s be clear. This means that, of all the coronavirus cases that have been closed so far in the US, 28% of them have resulted in death. Compare this with the comparable number from South Korea, which is below 2%. Do you think that might have something to do with the fact that they had fewer than 250 deaths, while we had over 55,000 deaths as of April 27?