Isn't the concept of herd immunity a bit absurd?

Perhaps I am greatly misunderstanding something, and if so, I’d appreciate it if someone would set me straight.

But when I see people touting “herd immunity!” in the context of the Covid pandemic (and they’re not talking about vaccinations, either, but rather, people getting infected) - isn’t that suffering the exact outcome (many/most people contracting the virus) that we’re trying to prevent?

It would be like someone saying, “I have a hive full of bees in my backyard. Since bees can only sting you once, then the only way to ensure that I won’t be stung by these bees in the future, is to go get stung by all of them, right now, that way they lose their stingers and die, and cannot sting me again.”

Well, it might be different for people of different risk categories. The vast majority of people who get COVID are asymptomatic - or, at least, do not require hospitalization.

As I understand, one big concern was to level out the rate of infections, so as to not overwhelm care facilities.

Your bee analogy does not impress me as terribly apt, but I don’t care to parse the logic.

The concept of herd immunity is not even a bit absurd…it’s reality. The way people are perhaps using it, or their extrapolation of it might be absurd, but not the concept itself.

It’s thought that something like 70% of the population needs to be exposed to the virus to achieve herd immunity. Ideally, you’d achieve this with a vaccine. In the absence of a vaccine, though, the only way to achieve herd immunity is for a large number of people to become infected, as you state. However, you would ideally want to spread the number of infections out over as long a time period as possible (by social distancing, face masks, avoiding gatherings, etc.) so that hospitals are not overwhelmed. Also, if you spread the number of infections out over time, you give the medical community time to develop more effective treatments and therapeutics, as well as (hopefully) a vaccine.

Remember all those huge spreadsheets of various mitigation tactics with the expected reduction in “R”? A lot of them had a way worse expected value than having even 10% of the population already immune. So it can’t be either completely discounted or completely relied on as the main means of mitigation.

Sure, herd immunity works fine. Assuming it takes only 40% of the population to get the disease that’s only around 6 million dead people at the current mortality rate. Sure, there will be many more people than that who are disabled long term, but like the other survivors they won’t be passing along the virus anymore. Maybe, because we don’t know how many people would need to be infected, or whether they will actually develop immunity even if the virus doesn’t mutate into something new.

But let’s just take a chance, we’re the right kind of people aren’t we? The virus won’t get us, it’ll get those other people. You know who I’m talking about right? -wink-wink-

A number of years ago, one of my children got the mumps. We vaccinated our children on schedule, so we were quite surprised, until I found out that the Mumps part of the MMR vaccine is only about 60% effective. Sounds pretty low, but…

The good news is that Mumps doesn’t mutate, so you can vaccinate now and you’re good to go. So, if everyone got vaccinated right away, the number of Mumps cases that year are 60% less than what they were before. There’s only 40% the number of cases out there, so the second season, there’s only 40%*40% = 16% of the number of cases. Season 3 is only 6.5%; season 4 is 2.6%; etc. etc. etc.

But what if half the people are anti-vaxxers. Well, then, you’re (in effect) making the vaccine 30% effective. So, the next year, you’re at 70% instead of 40%; the next, 49% instead of 16%; 35% instead of 6.5%; etc.

“Herd Immunity” means that there’s enough people out there that are immune to the disease that it can’t spread very fast or very far. Yeah, I simplified the math above, but it gives you the idea of how herd immunity works. The 70% number being thrown around comes from people much smarter than I who have a much better idea of the communicability of similar diseases, mutations, etc. Yes, without a vaccine, we would need 70% of people to either get the disease or to be naturally immune. And don’t discount the methods of curbing the spread. Face masks aren’t perfect, but they help. Washing your hands helps. Social distancing helps. Put them all together, and we can keep this down to a dull roar until a viable vaccine is created and distributed.

OK but you see other countries (such as New Zealand) basically taking the approach of “We will keep the virus out at all costs and keep infections to the bare minimum possible”…basically holding out until the vaccine arrives. Isn’t that a far sounder approach?

Sure, but it’s an approach that’s only available to a few places: High income islands with high social cohesion and functional governments with a plan.

The US can’t keep the virus out, it’s already in. We could maybe suppress it if we had a cohesive strategy to do so, enacted at many levels of government, and a population that wasn’t so partisan and contrarian that they’d actually wear masks. But we don’t have those things. So instead we’re going to flail around ineffectively for a while.

Exactly. Basically what it’s saying is that when 70% of the population is immune, then if there is an introduction of a disease to a population, then 7/10 of the people an infected person would meet are immune, and not going to spread the disease, which makes that R0 value extremely low.

That’s also why we’ve seen measles outbreaks in recent years. Dumb-ass anti-vaxxers have basically blown up the herd immunity by raising the number of people who can actually catch measles because they’re not immunized. Most of the time in modern life, herd immunity is more something that is relied upon for the immunocompromised or babies/small children.

The catch with it for COVID-19 is that getting to herd immunity would entail staggering numbers of deaths. The US population is roughly 330 million people. 70% of that is 231 million people. If we use the CDC’s 0.4% mortality rate, that equates to 924,000 people dying of the disease. Which for comparison purposes is:

  • A little less than the population of the state of Delaware
  • More than twice the number of US military personnel killed in WWII
  • About 200k more than the total Civil War deaths (on both sides)

That’s why herd immunity is not being taken seriously as a strategy against this, except by maybe the most non-empathetic analysts.

Also, since Covid immunity only lasts a few months, you’d have to have the majority of Americans reinfected again and again.

That’s still an unknown. Basically, if that’s the case, we are all probably screwed anyway, unless the subsequent mutations are less virulent. If that’s the case, then this virus will probably wipe us out…and wipe out anything else that can get infected, as herd immunity WOULD be out the door.

Herd immunity isn’t about why the herd is immune, it’s about the herd protecting those that aren’t immune.

As long as your definition of “a while” is “for the foreseeable future”

You’d think so, but both Paraguay and Uruguay have done remarkably well, despite both being neighbours of Pandemic Disfunction poster-child Brazil. National level coordination and, yes, a plan and belief in science, are probably the more critical factors.

And to bring it back to the OP, herd immunity makes sense across a run of years, but its really risky to get to the point where disease is endemic and being controlled by residual immunity or vaccination. Unless you are Samoa, measles pops up in small numbers, kids get it, a very small number get sick and the world moves on. Samoa was an example of where community immunity was retarded by a 50% drop in vaccination, and herd immunity was lost.

Mongolia, too. The US really can’t hide behind “we don’t have the sophisticated infrastructure to control this” excuse.

Let’s start with the understanding that there are several possible futures, and that different people assess the likelihood of each future differently.

One is the possibility that regions will be able to suppress SARS-CoV-2 infection rates to very low levels long term by some combination of ongoing social distancing, intermittent lockdowns as needed, comprehensive testing and contact tracing with self-quarantines, and isolation from imported cases by whatever means required.

Another possibility is a vaccine fairly quickly developed that safely provides good enough protection for long enough periods that is available to and accepted by enough people that herd immunity is achieved safely.

And the last is that infections occur to some segments of populations over some period of time resulting in regional herd immunity, or absent full protection at least protection from severe disease upon re-exposure and potentially decreased transmissibility. Under this possibility there is the possibility of controlling the who gets infected the most (protecting the higher risk while lower risk individuals build the pool of resolveds) and the when (as a surge that overwhelms systems or is timed with influenza, or flatter spread out over non-influenza times, for example) by impacting behaviors.

Note that if neither of the first two occur, for any reason, inclusive of failure despite best efforts, the third is what occurs.

Next let’s look at what is and is not known.

Not known is what level of infections is required for herd immunity in any specific society or region. 60 to 70% as the quoted guess is based on a belief that this germ would act like an influenza. It does not. the number is an unknown.

Not known is how many in any population function as not susceptible in any specific population. Studies on blood sample stored from years before the pandemic demonstrated that about 30% of samples contained T-cells that specifically respond the SARS-CoV-2 before the germ ever existed in human populations. Non-specific antibodies from other common cold causing HCo-Vs provide some protection against SARS and MERS and are speculated to do the same against SARS-CoV-2. Children, especially those 10 and under, seem to not transmit much even when they are sick with COVID-19, which may mean they function more similarly to non-susceptibles than as susceptibles in any model.

Not known is if those who have had asymptomatic infections some sizable fraction of whom do not have specific antibodies significantly elevated are susceptible or not by way of specific T-cell responses. Not known is how long protection from infection lasts. Not known is how significant mutation of SARS-CoV-2 will be and how either the state of having resolved from natural infection or having specific antibodies by way of immunization each do in that case.

Known is that a larger share of the population being susceptible will result in a faster building and higher surge than a smaller share, whether or not full herd immunity exists.

Known is that even a moderate surge occurring at the same time as influenza hits would overwhelm systems horribly and lead to many excess deaths.

Not known is whether either of the first two possibilities will occur, can occur, or what sorts of collateral damage attempting them might incur. Just not known.

Personally I would consider a plan that does not consider the possibility that the first two might both fail, and that does not hedge against that possibility with consideration of how to make the third alternative the least harmful possible, to be reckless.

It is baffling that so many think “lockdown, reopen, repeat until vaccine comes/disease goes away” is a perfectly safe way to go. We have to at least be prepared for the idea that those won’t happen or they could happen ten years from now.

Isn’t it conceivable that NYC already reached it?