August 7, 2020: Redefining (Herd) Immunity

 

Quick, before reading the news of the day, I want to talk about immunity! That’s because of a great Atlantic article by Ed Yong on this, with the charming title, “Immunology Is Where Intuition Goes to Die.”

It’s free, like all The Atlantic’s coronavirus coverage, and well worth your time. It will leave you feeling, for a few minutes, like you get it – not that you know the answers, because nobody knows the answers, but that you get the situation. For a minute, antibodies, and T cells, and B cells, will all make sense .

But the best part of the article is that it clarifies something even more basic. It turns out that “immunity” means something different to layfolk and to immunology folk. We lay people would like “immunity” to mean that someone can’t get the disease, either because they already had the disease, or because they had the vaccine.  We want it to be like immunity from prosecution! You can’t jail me for this, because I have immunity! In what Yong calls “the colloquial sense,” we want “immunity” to mean Nyah, nyah, nyah!

Immunologists, however, use “immunity” to mean that the immune system has a way, or ways, to fight the disease.  

Here’s Yong:

“Even the word immunity creates confusion. When immunologists use it, they simply mean that the immune system has responded to a pathogen—for example, by producing antibodies or mustering defensive cells. When everyone else uses the term, they mean (and hope) that they are protected from infection—that they are immune. But, annoyingly, an immune response doesn’t necessarily provide immunity in this colloquial sense. It all depends on how effective, numerous, and durable those antibodies and cells are.

Immunity, then, is usually a matter of degrees, not absolutes.”

A matter of degrees. There you have it. Do you have antibodies? How many? How good? (Apparently both quantity and quality matter.) Do you have T-cells that are suited to fighting this pathogen? B cells? Here’s another nice bit from Yong:

"Picture the lymph nodes as bars full of grizzled T-cell mercenaries, each of which has just one type of target they’re prepared to fight. The messenger cell bursts in with a grainy photo, showing it to each mercenary in turn, asking: Is this your guy? When a match is found, the relevant merc arms up and clones itself into an entire battalion, which marches off to the airways.”

You will read and maybe even interact with, all sorts of articles about “herd immunity,” including “A Vaccine or a Spike in Deaths.”

It has a fun interactive, with cartoon characters and little dots that change color, and a chance to “replay” the infection in populations over and over. But those articles still assume that someone with immunity is IMMUNE, not that, for instance, they have a strong immune response to the pathogen, which perhaps makes their disease course shorter or milder, but doesn’t keep them from being sick and also contagious. We are pretty sure that people who have asymptomatic or mild cases of COVID-19 are contagious, so it’s possible that vaccines will mean more mildly-ill victims (rather than severely-ill ones). But that doesn’t stop the spread.  

And then there’s the question of how long immunity lasts. Yong writes, “Immunity lasts a lifetime for some diseases—chickenpox, measles—but eventually wears off for many others.” We don’t know for sure, because it hasn’t been around long enough, but an impermanent “immunity” is not uncommon in respiratory viruses.

So. I’m rewriting Imperative #1. It used to say “We need herd immunity,” as if that were a destination, as if a magic number of immune folks would form a bulwark around those who were unable (and even those who were unwilling) to vaccinate.

It’s looking as if that “destination” model may be too simple. After all, a big fraction  of us can get a cold, and the next year, our antibodies having fallen off, a big fraction can get another cold. (Four coronaviruses (different ones) cause about one third of the colds we get every year. We are only immune for a short period of time after we recover.)

I want Imperative #1 to read:  We need more ways to give more people more immunity. Attempts at “natural” herd immunity have been disastrous, and as the interactive article shows, even if herd immunity WERE a destination, absent a vaccine, we’d have to endure an astonishing number of deaths* to get there. 

You see the three little dots on the left of the bottom row? We’d need to get from there (current deaths) to the nearly ten times as many dots on the right.

(*Yes, I know that focusing on death leaves out the many long-lasting effects seen in numerous COVID-19 survivors. I haven’t read a good overview or summary for lay people like me on the prevalence of sequelae, but I’m on the lookout. I have seen medical types saying “We just don’t know about how severe the long-term effects will be on survivors who suffered, for instance, circulatory system damage, and many or most survivors do.” I’m sure one of these days we will know much more on that count. )

The only good way to make the herd more immune without a lot of people dying (and suffering those long-term health effects) is via a vaccine, or a bunch of vaccines. Imperative #1 has effectively merged into Imperative #5: We need tools: (vaccines and treatments, tests and tracing, and of course, decent and accurate numbers, with which to measure what is happening.