Because…a lot of people aren’t really quite getting it. Maybe this will help.
Imagine that you own a bar. You have a bouncer who’s job it is to remove anyone who is getting too drunk and causing too much trouble. Let’s call him Steve.
There’s this no good guy in town called Covid. So, let’s go through some scenarios.
It’s a reasonably bustling Thursday night and this stranger from out of town comes in, has a few drinks.
He becomes belligerent and starts trashing the bar before Steve can react. In fact, this guy is so much trouble he gets behind the bar and starts breaking top shelf bottles.
Your bar is so damaged it has to close for a while or, worse, permanently. Steve wasn’t ready for this!
You finally get your bar open again. Covid walks through the door. Now, at this point, Steve knows who he is and can try to remove him right away.
He might succeed.
He might get into a fight and flip a table.
Or he might get his butt completely handed to him; but it’s much less likely that he will now he knows who Covid is and that he’s only there to cause trouble.
But Steve can’t actually do anything until Covid enters the bar. Now, if Steve is really, really on the ball maybe he’ll wait outside and deal with him outside.
All of these scenarios map to infection-acquired immunity! Neutralizing immunity, where you don’t get infected at all (Steve stops Covid in the street) is the rarest. Most likely, you still get infected but because Steve is ready for Covid this time, he can deal with him with much less damage. You don’t have to close the bar.
Word on the Street
Now, let’s imagine that this Covid guy has been working through all the bars in town and trashing them.
Sooner or later, word would spread. Somebody tells Steve to watch out for the troublemaker.
Covid walks into the bar. Because Steve has been given a good description of the guy, he has a chance of recognizing him and throwing him out even though he hasn’t met him before.
Maybe he can stop him at the door. Maybe he can remove him after he enters. Or maybe they get into a fight and flip a table.
And, yeah, he might still get his butt handed to him.
It’s still much more likely, and the advantage is that you didn’t get your bar trashed the first time.
Yeah, that’s vaccination. Vaccination doesn’t necessarily keep you from being infected. It might let you get infected, but significantly reduce how sick you get…turning COVID-19 into a regular cold.
Now to two rarer scenarios.
Let’s imagine that our no good out of towner, Covid, has four equally no good relatives in town. Let’s call them Eric, Neil, Ozzy and Henry.
Steve sees Covid and goes “Well, huh, that guy looks an awful lot like Ozzy, and we banned him last year for causing trouble. I’m going to keep a special eye on him.”
When Covid starts to cause trouble, Steve tosses him out after he’s only trashed a bit of the bar, because he already suspected he was no good based off of his family.
This is called cross-reactivity, and it may be a thing. (Eric, Neil, Ozzy and Henry represent the four existing human coronaviruses that cause colds. Ozzy may have been a real troublemaker in the past!). Exposure to other coronaviruses primes your immune system to potentially recognize SARS-CoV-2.
The Overactive Bouncer
Last time Covid was here he trashed the bar. Steve is really, really mad about this.
When Covid shows up again, Steve beats him up…
…and Steve trashes the bar.
There’s something called “antibody dependent enhancement,” where having antibodies to an infection actually makes it worse.
Good news: If antibody dependent enhancement was a significant problem with COVID-19, then treating people with convalescent plasma would make them sicker. This isn’t the case, so we probably don’t have to worry about it with this virus.
So, does that help people understand how immunity actually works? It’s not as simple as “Immune means you can’t get infected.” But it’s still the key factor in how we’re going to keep Covid from trashing all the bars.