[nudephil (OP)]

Here's a question we've had in from listener David:

For years now we have been saying we should let kids out to play more and that cuts and bruises don't do any harm. Also kids don't contract the diseases/infections we used to.

Could this be a factor in why younger people seem to get COVID more mildly? Their bodies are presumably quicker at identifying rogue cells etc. We older people have had numerous infections so our bodies must be less able to make the distinction between very harmful and minor infections.

Does the body learn from exposure? And if so, does it follow that a little knowledge is a dangerous thing - i.e. does the immune system take longer to recognise the infection because it mistakes it for something else?

Any thoughts?

[Colin2B]

It may be the opposite. Children in particular regularly get colds (coronaviruses) and it is thought that this might alert the immune system - particularly the T cells - to that type of infection.
But, the main reason is that their immune system is more robust, they are quicker to repair damage, tissues eg lung tissue are more flexible and resilient, and they have fewer of the serious risk factors that affect older people eg diabetes, COPD, dementia, frailty.

[alancalverd]

Three conflated notions in the OP.

Yes, a bit of exposure to dirt in childhood is essential to prime the immune system, and if you've never grazed a knee you won't learn to take care in late life.
But

kids don't contract the diseases/infections we used to

is due to the eradication of most infectious diseases, vaccination, hygiene, and nutrition.

COVID primarily impairs respiration. If you have generally good health and plenty of "spare" lung capacity you may recover, or even not notice a temporary decrease in  capacity, but if your cardiopulmonary function is only marginal and you have difficulty breathing when recumbent (eg from obesity or general lack of muscle tone) you are likely to decline and probably die from some other respiratory disease such as pneumonia .