What does "Immunity Debt" mean anyway?
What does "Immunity Debt" mean anyway?
Immunity debt is a new phrase based on an old idea. When your immune system comes into contact with a antigen - bacteria, virus, whatever - it produces an adaptive immune response to fight off the infection. Specifically, it manufactures T and B cells, which defend against the infectious disease.
The molecular biology here is complicated, but the simplest explanation is that the T and B cells are specific to the exact infectious disease that the body is facing. They’re not all-purpose. They fight that exact infection. When you are exposed to something for the first time, your body has to produce a brand new immune response. It takes time for for this to happen, and in that time the pathogen can infect you.
If you’ve been exposed, before, though, your immune system remembers the pathogen. The immune response is fast - so fast you don’t get sick.
This means that lots of minor exposures to infectious diseases help prime your immune system. You’re ready to immediately produce T and B cells for just about anything.The idea of immunity debt is that if you go a long period without exposures, you become more vulnerable to infections, because your immune system’s memory fades quickly.
The idea of immunity debt is that if you go a long period without exposures, you become more and more vulnerable to infections, because your immune system’s memory of some infections fades quickly.
I don’t really know why we use the term “debt,” but that is what “immunity debt” describes. You went too long without being exposed to diseases and now you owe someone - Fate? God? The CDC? - a whole bunch of illness.Therefore, pundits argue, everyone is sick in late 2022 because we were too good at avoiding exposure to illness. Our masks were too helpful. Our careful distancing worked too well. Now we’re all in debt to the sickness gods and we are paying the price in disease. These two articles, in Slate, and in Wired, do a good job of laying out the immunity debt concept.
Personally, I am not convinced. (Please note that everything from here on out is just my own opinion and speculation, based on what I know in early January 2022. It’s me looking at the science and sharing my guesses but it’s not fact, or science.)
The theoretical immunology of exposure and response is correct. And it works if we’re talking about babies. Toddlers who’ve been protected vigorously from infection for their entire two-year lives are very vulnerable to getting sick. It’s the same phenomenon as sending a child to daycare for the first time and they spend their whole year getting sick.
However, it’s not just little kids and babies getting sick right now. Adults are getting influenza and RSV and on top of that all kinds of crazy infections we’re not used to thinking about. I think adults are getting infected in numbers too large for it to be immunity debt. This wave of illness is just too big.
In addition, both kids and adults are getting very, very sick. Lots of mild illness could be immunity debt; lots of severe illness looks like something else to me. There is no reason that immune debt would make RSV infections worse. More common, yes. Worse - no.
It also seems to me that the US COVID infection numbers don’t indicate we did a particularly good job of avoiding exposures to illness. If a wave of illness was hitting China, or Vietnam, I would think it could be immunity debt. People really did avoid exposures in those countries. But the US? I am not convinced most American adults were ever protected enough to incur an immune debt.
The grim alternate explanation is that having had COVID makes us more susceptible to future infections. Right now, the data is inconclusive. Some studies say that COVID weakens the immune system, some studies say it doesn’t.
My guess, however, is that in a couple years we’ll see that a past COVID infection puts you at greater future risk for infections of all kinds. I would prefer the immunity debt scenario. It’s the easy, comforting explanation. And it may well be true. But I am not going to depend on it.
One final note. As I’ve mentioned many times before, I’m not an MD or a PhD. I have an MPH and I’ve spent the last 20+ years running global health programs, but that doesn’t make me a scientist. But I do know some scientists, so I wrote to my friend Edsel.
Dr. Edsel Salvana is an infectious disease specialist, molecular epidemiologist, vaccine researcher, director of the Institute of Molecular Biology and Biotechnology at the National Institutes of Health at the University of the Philippines in Manila and an Adjunct Professor for Global Health at the University of Pittsburgh.
Here is what Edsel had to say about the concept of immunity debt:
“I don't think 'immunity debt" has any good scientific basis as I understand it from what articles I've seen. In general, the immune system isn't a zero sum game where the longer you don't get infected, your next infection will be worse.
What if you die from the first infection? It's such a misguided concept used to justify "natural immunity" when vaccines and masks are there that have so much more benefit versus the downside. That's why vaccines were developed in the first place so you don't die from the infection.
And masks, even if they sometimes fail to prevent infection still decrease inoculum size and can decrease the severity of illness. I just feel there is so much pseudoscience at work when "immunity debt" is discussed that it confuses many people and plays right into anti antivaxxer narratives.”
Yep, that’s how vaccines work.
You know what else is a minor exposure that primes your immune system, VACCINES. I realize that anti-vaxxers probably don’t read this newsletter, but maybe the talking points are useful to someone anyway?
Why not just expose ourselves as much as possible then? The problem is that your immune system is totally a superhero, but it’s like a Spiderman or Ms. Marvel superhero. Impressive, powerful, extremely cool - but not omnipotent. The immune system can be defeated. Spiderman takes down neighborhood criminals just fine, but Thanos had no trouble blipping him.
Some immune exposures are minor and make your immune system better prepared. Some immune exposures mean you get infected. Mostly you recover from infectious diseases. Sometimes with no real effect, like the common cold. Sometimes you recover but you’re disabled for life - polio. Sometimes you live with the infection forever, like HIV or herpes. And sometimes you die.
With some infections, like measles, your immunity lasts your lifetime. With others, like the common cold, you can be reinfected in a few months.
Here is a list of his 72 publications: https://scholar.google.com.ph/citations?user=gvZUQysAAAAJ&hl=en.
Thanks for this! I looked up “immunity debt” after you last post and have been thinking about it on and off since then. So I’m glad you wrote something about it. The idea of an immunity debt seemed plausible to my admittedly unscientific self, so I wondered why you weren’t buying it.