Sunday, March 15, 2020

Episode 33: The Ironies of Herd Immunity (Demographic Doom podcast script)

This is the script for my Demographic Doom podcast episode (#33) released on 15 March 2020. It may differ slightly from the final broadcast. This episode is available on major podcast platforms, including PodbeanApple Podcasts and a video version on YouTube. See the description on the YouTube version for annotations, links and corrections. You can also comment on this episode there. (If you leave comments on this blog post, I might not see them.) The main website for this project is

I’m Glenn Campbell. I call myself a demographic philosopher. I’m looking at life and trying to predict the future through the lens of demography, or the study of human populations.

Today is March 15, 2020—the Ides of March—and I'm talking once again about the Covid-19 epidemic that is now sweeping the planet. In this episode, I want to talk about one demographic aspect of this disease: something called "herd immunity". This concept is important because it tells us something about when and how the epidemic is going to end.

Regarding the virus, you may have heard people say, "This thing is spreading so fast that eventually everyone is going to get it." This is simply not true—at least with a viral epidemic as opposed to a bacterial one. No virus can ever achieve a 100% infection rate. Unlike a bacterium, a virus is passed from person to person and can't survive or reproduce on its own. Virus particles are shed by one person and picked up by another, but this has to happen quickly, within a couple of days, or the virus particle disintegrates. A virus can't "attack" anyone. It can only float around in the air or stick to a surface until someone inhales it or otherwise takes it in. The virus then hijacks a vulnerable cell and turns it into a virus factory, which spews out more little particles to be inhaled by someone else.

If someone is infected by a virus, two things can happen. Either they die, or they fight off the virus and gain immunity, at least to current version of the virus. Their body has learned to detect and neutralize the virus so it can't infect them again.

Herd immunity means that enough members of the population have already gained immunity that the rest don't have to worry anymore. For example, if the neighbors living on either side of you get the virus and recover, then you can no longer catch the virus from them. They are unlikely to be reinfected, so they can't pass the virus to you. If you are surrounded by enough people with immunity, then you are essentially immune yourself, because there's no one to give it to you.

Of course, a virus can mutate over time, which is why we can get the flu every year, but for each specific version of the virus, you either die from it or you gain immunity. If enough people gain immunity in a given population, then the others are protected. I can't tell you what the percentage is. It differs by the virus and the countermeasures taken against it, but this number exists, and once that proportion is reached, the virus begins to die out.

Herd immunity is connected to the "R-nought" or the infectiousness of a virus. In the case of Covid-19, the R-nought is said to be somewhere between two and three. In other words, under current conditions, each person who catches the virus gives it to, on average, between two and three other people. This isn't a fix number, however. It can go up and down with the circumstances. If one infected person sneezes on a dozen people, their personal R-nought is quite high, but if most of those people are already immune, then the R-nought remains low.

Once the R-nought falls below one, then herd immunity kicks in. If each person getting the virus gives it, on average, to less than one person, then the virus eventually expires. There may still be people in the community have never had the virus and are not immune, but the virus can't get to them because it has run out of carriers.

So how many people need to catch the virus to confer herd immunity on all the rest? This is a matter of debate. Mathematically, it's something around 60% for this virus, but this is a moving target, because people can change their behavior, and consequently their R-nought. Right now, in the early stages of the epidemic, the R-nought is between 2 and 3, but this will decrease with time, both because more people become immune and because people have changed their behavior so they are less likely to contract and pass on the bug.

What this means in practice is that the number of people required for herd immunity is probably less than the 60% mathematical ideal. I'm guessing only about 40% of the population will be getting the bug, because I see that so many people around me are getting paranoid about hygiene. So long as everyone in society is desperately trying not to contract the disease, fewer people overall will get it and fewer will die.

In other words, it is NOT inevitable that you will get the disease. If you can maintain a high level of hygiene for, say, the next year, you could skate through this without ever catching it. Eventually, enough members of the herd will be infected that the R-nought falls below one, and the rest of the population is safe.

Herd immunity has a lot of practical implications, some of them rather unexpected, so let me talk about the ones I've thought of.

The Number One implication of herd immunity is that it is not inevitable that you will get the disease, On the whole, I'd guess you only have about a 50% chance of getting it, give or take, assuming you are careful.

To a large extent, whether or not you get the disease is under your control. You don't have absolute control, but you can shift the odds in your favor by changing your behavior. I'm not going to get into what those changes should be, but you've heard about them in the media: wash your hands frequently, be careful what you touch, don't touch your face when your hands have been tainted, etc. Everyone has to come up with their own hygiene plan, but if yours is smart and effective, you can greatly reduce your chances of getting the disease, and consequently you'll reduce the chances of someone else catching the disease from you.

Each person has a lot of discretion. They can change their behavior so they are less likely both to get the bug and to give it to others. In this way, your own behavior contributes to the health of your entire community. It is one case where your own personal self-interest coincides with the interests of your country. By practicing good hygiene, you're not just protecting yourself, you're also helping to protect others.

But there is also a non-altruistic angle to herd immunity: Even if it's not in your self-interest to get the disease, it is in your self interest to have others get it, because you need them to protect you.

Let's imagine you're a brutal dictator, like Kim Jong-un of North Korea. You know the virus is raging through your country, and you don't want to take the risk of dying from it. If you were ruthless and you understood epidemiology, you could systematically go through all the people in your inner circle and order that each of them be deliberately infected. While they are infected, they are sent away to quarantine, where they either die or gain immunity. Once they have gained immunity, they would be brought back to your inner circle. Eventually, everyone around you would be immune, and you couldn't get the disease because there would be no one to give it to you. Of course, a certain percentage of your inner circle would die, but you personally would be protected.

The same logic applies in the rest of the world. It is in your own best interest to not get the disease. But in the long run, it is also in your best interest that other people do get it, because it helps build up herd immunity that will protect you. From a purely selfish standpoint, the best outcome is for all your neighbors to get the virus but you don't.

How would this be expressed in the real world? Let's say you buy up all the hand sanitizer at you local store, until you have way more than you need. This increases the risk for other people in your neighborhood who now can't get hand sanitizer. Nobody thinks, "I want to screw my neighbors," but that's effectively what's happening. By buying too much hand sanitizer you are essentially encouraging your neighbors to get the disease which will eventually protect you with herd immunity.

In one sense, we're all in this together. No one wants this thing to spread so fast that it overwhelms medical resources. In another sense, we are all competing with each other to survive. Everyone wants to be among the 50% who never get the disease and who are eventually protected by the herd. It's not an overt conflict, and most people aren't conscious of it. It's more a sense that, "I'm going to avoid this thing, because I have better hygiene than you."

Right now, on March 15, the Covid-19 epidemic is just getting started in the U.S. Less than 50 people have died so far, and nobody knows how many have been infected because testing has been so limited. Certainly everyone is talking about it. I was in an airport yesterday, and as I listen to snippets of conversation, it seems like most travelers are talking about the virus and what they're going about it. This is a major shift from just 3 weeks ago, when the virus was a news story but hardly anyone on the streets of the U.S. was talking about it.

From overhearing these conversations, I have come to realize that everyone has their own hygiene plan, and they can vary greatly from person to person. Some people are wearing face masks, thinking this is their best means of protection. Others are eating garlic, because they think that's going to help them. Personally, I'm a surface guy. I focus on the surfaces that my hands touch and how to protect myself from them. Some people get really paranoid and go into full bunker mode, while others refuse to do anything at all. They believe the virus is no big deal, so they see no reason to modify their behavior,

A person's hygiene plan and how well they implement it are a reflection of their personality, so there are as many plans are there are people. Once someone has settled on their plan, it's hard to dissuade them of it. If they think garlic is the way to go, you got to let them follow their path. If they're going to hoard toilet paper, let them do it. Like other aspects of personality, any evidence you offer probably isn't going to change their mind.

In the long run, though, some hygiene methods are better than others, and the virus itself will decide what works. Those people who are eating garlic in lieu of other precautions are more likely to be struck down, while people who can think rationally and put themselves in the position of the virus are more likely to survive.

It is often noted that two classes of people are disproportionately affected by the virus: the elderly and people with pre-existing medical conditions. I propose a third class who will be disproportionately affected: stupid people. No one can be blamed for catching the disease in its early stages, because none of us were prepared, but once you do have time to prepare, a lot more of the burden falls on you. You can do everything right and still get the disease, but your risk is greatly reduced. On the other hand, if someone does nothing right, taking no precautions whatever, their risk remains elevated. If your hygiene plan is stupid, you're more likely to get the disease and more likely to die, which has a certain Darwin Awards justice to it. The virus is going to take out a lot of old and sick people, through no fault of their own, but it's also going to take out a lot of stupid people who should have taken precautions but didn't.

So that's one of the societal conflicts right now. You have smart people competing with stupid people to be among the 50% who will eventually be protected by herd immunity. Getting the disease doesn't prove you are stupid, because you can never reduce you're risk to zero, but all other things being equal, the stupid will bear the brunt of this disease. They will choose an ineffective hygiene plan and catch the disease. Then they will either die or provide the herd immunity that protects the others.

So here's another crazy idea that's raised by herd immunity. We know that the young people are relatively unaffected by the disease. Around the world, very few children have died, while people in their twenties can almost laugh it off. So how about we deliberately infect all of those young people to contribute to herd immunity? I know it's not an acceptable politically, but from an epidemiological standpoint, it would theoretically help.

The standard policy now is to close schools in any area where the disease is suspected. This may be the right political decision, but I don't think it is backed up with science. Where are these children going to go? Lacking adequate adult supervision, they are probably going to congregate with each other and could still pass the disease among themselves and eventually pass it to their more vulnerable elders. A more sensible solution, scientifically but not politically, would be to bring them to school, lock the doors and deliberately infect them all with the disease. You keep them there for a month or so, until they are no longer contagious, then you release them into the community again. Now they can't infect anybody. In the long run, this would mean few deaths overall. Those who are vulnerable would be less likely to get these disease because there will be fewer infected children to spread the disease.

You can do this sort of thing with a population of rats or livestock, but you can't do it with people. The irony of quarantines, closing schools and many other political interventions is that it may be making things worse overall. Politicians are making the decisions, not scientists, and politics is a very short-sighted endeavor. Politicians are trying to read what the public is feeling and are responding directly to those feelings. No politician could tell parents, "We're going to put your child at risk to protect some old people." In a political environment, any deliberate imposition of risk is unacceptable, which really cripples the whole political system is a situation like this.

So what we're left with is hysterical lockdowns and closings without any real analysis of what the long-term effects will be. I suspect that the most effective counter-measure to the virus is the more laissez-faire approach that America seems to be pursuing. Everyone is responsible for their own health and hygiene. I think that for the most part, people are paying attention. I see people opening doors in new ways so they don't have to touch the handle. If enough people are behaving this way, it's probably going to do more to reduce the R-nought than any government program or quarantine.

And here's another crazy idea: Donald Trump's incompetence might actually be helpful. As you may know, the response of the Trump administration to the epidemic has been less than stellar. Trump himself has called the epidemic a hoax and blamed it on his enemies. I'm not saying I would want an incompetent leader, but there are some potential bright sides. A big one is that the U.S. could avoid some of the desperate "bargaining" actions that other countries have taken.

You've heard of the Five Stages of Grief. They are denial, anger, bargaining, depression and acceptance. Donald Trump is stuck in the denial and anger phases, which are the only things he really knows how to do, and this may be good, because the bargaining phase can get very expensive. Bargaining is when you grasp at any kind of straw to try to make the problem go away, and often these straws are very costly.

Italy, for example, has locked down it's entire country, trying to ban travel and get everyone to stay home. I have doubts about how effective this will be, but it is devastatingly expensive for the economy. Closing schools here in America is also an expensive move, putting a huge burden on parents in exchange for unproven gains. These are examples of bargaining, or desperate attempts to restore order with dubious results. The Trump Advantage is that his administration is so crippled that it may not have the opportunity or wherewithal to pull off many of these desperate moves.

If a competent administration had been in place, it might already have implemented quarantines, like cordoning off sections of Washington State. The competent President would have reassured the nation with his or her speeches, while Trump just stokes more panic with his. The net effect is that nobody trusts the government to protect them. This may be good, in that it forces people to rely on their own resources. Everyone is realizing, "Only I can save myself," which gets them focused on the practical things they can do to avoid the virus. In the end, this might be more effective and less costly than any government initiative.

One way or another, we have to achieve the stable state of herd immunity, where a certain proportion of the population has gotten the disease and the rest are protected by them. If people, on the whole, are paranoid about their own safety and follow effective hygiene protocols, it is better for society because it means the R-nought is lower and fewer people have to get the disease to achieve herd immunity. Trump may actually be helping things if he stokes paranoia and gets people panicked, because you want people to take action. At this moment in history, a competent, soothing voice in the White House might actually be a bad thing if it lulls people into a false sense of security.

I don't want you to think I'm a Trump supporter, but sometimes an idiot can be useful.


For annotations, links and corrections, see the description on video version of this podcast. You can also leave comments there.