Auntie Cipitation. She is retired and a healthy person. She’s a solitary person and content to be. She goes to Dr and vet appointments and to the grocery store. She shops at a military commissary so can’t opt for grocery delivery. Occasionally out to eat.
You mentioned that she always masks, rarely goes out, has no currently known immune deficiency, and yet keeps getting sick.
There are so many variables in that statement to consider before assuming that her masking and isolation are causing her immune system to forget the immune memory it has built up over the last 50 plus years of her life (since you say she is of retirement age).
This is not meant as an attack on you--what I want to do is bring up all the variables that factor into what could be happening in her situation. I'm not listing them here as questions that I'm somehow insisting you answer to me, with documented details. It's a discussion/list.
This is all drawing on my experience of both me and my 17 yo having long Covid, both my kids having an autoimmune disorder that makes their immune system overreact to being triggered, and the fun new autoimmune disorders that have popped up for me since having long Covid that I definitively tested negative for before (as part of trying to figure out what was going on with my kids). I have spent a lot of time with a variety of rheumatologists, endocrinologists, and other specialists.
1) has no known immune deficiency--has she been tested for immune issues and everything comes back negative? Never been tested but assumes she has none? Immune deficiency means a pretty specific thing, medically. Autoimmune issues can pop up in a wide variety of ways--people with over-reactive immune systems can end up having bad reactions to different triggers and look like they are sick with something when they actually aren't, for example.
2) keeps getting sick--can mean a lot of things. Tests positive at the doctor's office/home tests for flu or RSV or Covid? Doctor says "looks like you have a some kind of bug," gives her antibiotics, and her symptoms improve, thus supporting the doctor postulating that she has a bacteria caused illness. Feels ill, but doesn't go the doctor, eventually symptoms resolve?
3) masks everywhere but keeps getting sick--if she is truly getting ill with different viral or bacterial caused sicknesses, then she's obviously being exposed somehow to these bacteria/viruses. Mask quality and fit could be an issue. If her mask fit and quality are good, then the issues in point 1 and 2 would have to be looked at.
Example:
If I didn't know I had long Covid, I would appear to myself and others much as your friend does (if her bouts of sickness are not being confirmed by testing/doctor) as being frequently sick despite masking. I have a sort of baseline of long Covid symptoms that are present at that level every day. And when I flare up, I exhibit many typical symptoms of being "sick"--to the point of even having fevers. But because I have to keep such close track of my health and daily activities and have been tested for flu/RSV, etc., my doctors and I are able to see the links between different triggers and the flareups.
My 17 yo, who has long Covid and an autoimmune disorder that makes his body attack itself whenever his immune system is triggered and overreacts, masks at all times in public but yet would appear on first glance to be sick a lot. Instead, for him, it can be something as simple as him leaving his bedroom window open for a few hours on a spring day to cool off his room triggering his seasonal allergies which makes his immune system charge in with all guns blazing as though he had just been infected with Ebola. He rarely ever gets actually sick, but you wouldn't know it because his immune system overreacts more than a Twitter user on a Friday night. It's like sending a SWAT team after one person...but once the SWAT team takes out that person they just keep going, lay waste to half the apartment complex, and end up hooting each other in their blind rage. And that was before he had long Covid....now that overreaction makes the long Covid symptoms 10x worse.
Immunity debt (in adults, not talking about children) due to masking/lockdowns/etc popped up in social media discussions over the last few years. Many virologists and other members of the medical community say that it is a flawed theory because it ignores so many different variables, some of which I discussed above.