How often does the adaptive immune system "learn" a new pathogen?

Question

I was arguing with an anti-vaxxer (clearly a favorite pastime) when he made the argument that there are certain risks, like triggering of autoimmune disease, inherent to the process of the adaptive immune system "learning" a new pathogen (memory B/T cell formation, etc.). His argument is that by administering vaccines, we are causing the body to "learn" new pathogens at several times the normal rate, thereby increasing the number of exposures to these risks.

While I'm thoroughly pro-vaccine, there is some truth to there being risks to "learning" new pathogens, with devastating diseases like MS, lupus, and rheumatoid arthritis commonly triggered by viral infections (though not as commonly as, you know, dying of diphtheria). Human parvovirus B19 for instance has been specifically linked by numerous studies to development of these diseases. I can't counter his argument without knowing more about how often a typical American or European adapts to a new pathogen, but I've found references to this information very difficult to track down in the literature.

So how often does the typical American/European "learn" a new pathogen, specifically meaning the adaptive immune system beginning the process of forming memory immune cells targeted toward a new pathogen? Once a minute? Once a day? Once a year?

Answer 1

I'm a little leery of answering here since it's difficult to address the specific postulate in the question. But hope this helps!

But that's kind of the point - your Anti-Vaxxer foe probably uses this argument because it doesn't get dismissed with data, so they think it's a win for them.

It's not of course - because them arguing that you can't provide data disproving their claim holds even more so in reverse. Or to put it bluntly Hitchens' Razor applies:

That which can be asserted without evidence, can be dismissed without evidence

In other words if they want to tell you that the vaccination schedule they are criticizing is "causing the body to "learn" new pathogens at several times the normal rate" then it's on him to provide information as to what the "normal rate" is for the body. We know the body encounters thousands of pathogens every day just in daily life, breathing, eating etc. (NB: I did have a great link for this but it seems to have rotted since I last needed it, will edit in if I can find a replacement) but how many of these are novel to the body is harder to know, obviously one day one they're all new but assuming the environment is reasonably consistent it's going to level off to some degree.

The numbers of "new" antigens introduced to the immune system through vaccination actually significantly decreased during the 20th century as vaccination technology and our understanding of the immune system improved, even as the number of actual vaccinations (and diseases protected against) increased.

The argument your anti-vaxxer foe is bringing out is essentially nothing more than the tired old "too many, too soon" trope with a bit of tinsel stuck to it. While it doesn't specifically address the question you're asking the Glanz et al study did a great job of addressing the more general version of the trope - that the number of vaccinations "overloads" the immune system and makes the person more vulnerable to other infections (spoiler alert: it doesn't), the publication of that (and others) is possibly the reason why the trope has mutated into the variant you encountered.