We actually need germs go to train and exercise our immune systems.
Look up the hygiene hypothesis.
Look up the hygiene hypothesis.
This is a widely held but incorrect belief. The immune system does not work like a muscle - it doesn't atrophy when unused and it doesn't become stronger from repeated challenge.
The immune hypothesis is about specific kinds of pathogens - parasites and bacterial microbiota[1] that humans co-evolved with and have specific defenses against (such as IgE antibodies). The exact mechanism(s) have yet to be determined but it's clear that lack of exposure during early childhood increases risk of autoimmunity.
Other than that, getting exposed to a larger variety of pathogens - especially viruses - just means you get sick more frequently[2].
The frequency of exposure to modern human viruses are a relatively new occurrence and there's no evidence that it benefits health - quite to the contrary, viruses are implicated in the pathogenesis of autoimmune diseases such as ME/CFS or MS.
The immune system can't function against viruses it's never encountered, and the health of the immune system does, in fact, rely on exposure.
No need to start licking doorknobs or whatever, but people who have isolated themselves in a comprehensive way from the common human biosphere should expect to get sick when they decide to rejoin humanity. This will get worse the longer it's put off.
I'm nonjudgemental about the choices people are making to mitigate risk in their lives, but declining immune system health is a real risk of extended isolation which should be factored into the decision-making process.
Two things happen when someone is isolated from that ambient biome: they stop producing as many antibodies and t-cells, and they miss opportunities to develop immune response to new mutations as they arise.
In the worst case someone can be hit with a variant of, say, influenza, with an already depressed immune system facing more immune-evading mutations than they would otherwise see in a novel strain.
None of this is controversial.
The isolated (isolationist has an implication of ideology which I don't care to impute) person can expect to get sicker for a given amount of exposure. Given a (spherical, frictionless) Person of Ordinary Health, they will have hundreds or thousands of distinct exposures in a year and get sick once or twice.
I could ramble about my own exposure to influenza, its relation to extended stays in the tropics, and so on, but this discussion doesn't need to be carried on the strength of anecdote.
The strategy should be to avoid severe outcomes. Long Influenza is a real thing and tends to follow severe infection, people who end up in the hospital with flu often have problems for years afterward, or the rest of their lives.
Vaccination (ceteris paribus again!) is superior to infection and raises the odds of transcribing new mutations to the immune system without ever getting sick. But there isn't always a vaccine, influenza in particular is notoriously skilled at vaccine evasion, and the immune system has a sweet spot in terms of antibody and t cell concentration which is kept in homeostatis by exposure and only exposure. that's how vaccines work, it's controlled exposure, nothing more.
Edit to add: so if you're someone who has isolated yourself from the rest of humanity's biome for a few years, I'm sure you had your reasons and I don't question them. It's probably not a lifetime's worth of strategy, and when it comes time to get back into it, be smart about it.
Maybe don't go straight to New York and ride the subway for eight hours without a mask. You wouldn't go back to the gym after a year and try and squat what you were pushing then, it would snap your spine. Same thing with rebooting the immune system. Slow and steady, and realizing that a mild infection (could be covid, rhinvirus, influenza, for our purposes this doesn't matter) is inevitable and doesn't constitute moral failure.
Citation needed. In what way is it worse?