I keep coming back to immunity in my thinking around Covid, because we’re continually forced into a dumb…

I keep coming back to immunity in my thinking around Covid, because we’re continually forced into a dumb binary between immunity and prevention of infection. Social media does that, it turns every issue into a binary, with a team at each end slugging it out. /1

The problem with immunity for me is that the closer you get to understanding it, the more elusive it gets. I think it’s not unfair to say that the most common public perception, but often also expert perception of it, is as a property of an individual. /2

A level of activation of an individual’s immune system, against a particular pathogen. This has never sat comfortably with me, because in its essence the immune system itself seems an open system, continuously shaped by encounters with the world outside an individual. /3

It’s an ecological space, a place of encounters between organisms and their associated microbes with the microbes that surround them. Even concepts like herd or hybrid immunity, which seem more open to this ecological interaction between individuals, don’t seem quite right. /4

Those concepts still heavily rely upon an idea of individuals and their immune systems, and if you just add up lots of them they can sometimes prevent infections from spreading. There’s not the sense of immunity more generally being an ecological relationship *between* them. /5

I did find the field of ecoimmunology which does take a more ecological approach. Though the basis of the field seems to be trying to understand individual variations in immunity, so still maybe grounded in individuals and their immune systems. /6 https://t.co/9sT519F7LF(Fig.

I liked that this field at least has a broader understanding of an immune response, stretching across multiple systems of the body, and also out into the ecological relationships between organisms. And its recognition of immunity as a last line of defence. /7

Which if used as a front line of attack risks autoimmune responses from the organism. Which goes healthily against the approach we’re taking with Covid, of trying to use immunity as a magic airbag of protection. But when you zoom out from all of this, I think it gets simpler. /8

Looking at ‘sterilising’ vaccines, and that they mostly don’t offer magic sterilisation but just reduce viral load so much that transmission is significantly reduced, it struck me that immunity and prevention of infection are actually the same thing. /9

That instead of seeing immunity as a way to buffer us from pathogens, it’s more accurate to see it as just one more way we prevent those pathogens from infecting us in the first place. Like a fire alarm in a building, not there to stop fires but to keep us away from them. /10

The older idea of ‘immunocompetence’, as some level of protection against a pathogen, misses this wider networked picture of a much more vital avoidance of infection. A medieval city that lifted the drawbridge and hoped the castle walls and moat would keep the invaders out…/11

…was using its last line of defence against invaders. The ultimate aim was always the same, to keep invaders out of that city or society. Not to live with the invaders, while safe behind walls and moats. This is the subtle but profound shift in framework I see with immunity. /12

We’ve pulled it out of its networked, ecological context and made it into something that it isn’t. It always was just one more networked way to repel invaders, to keep them OUT of us. Not a way to help us live with them. The point of ‘hybrid immunity’ for example? /13

It isn’t to make each individual just immune enough to live with repeated infections. It’s to make enough individuals immune enough that they stop spreading the infection to others, so that again the ultimate aim is to *prevent infection*. To keep the invaders out. /14

Putting to one side that many probably rightly believe hybrid immunity is a fantasy for Covid anyway, because of the nature of the virus and its uncontrolled spread. The concept of immunity itself has been isolated from its wider origin and function. /15

We don’t so much vaccinate to prevent individuals ever getting sick, or rather we do, but not by building them immune walls, drawbridges and moats. Vaccines boost that last line of defence, that’s all. /16

We need the front line of attack to be stopping the invaders ever reaching the walls of the castle in the first place. The whole game is the prevention of infection, immunity is one part of that single (not binary) process. /end