[1]https://news.yale.edu/2020/09/04/common-cold-combats-influen...
[1]https://news.yale.edu/2020/09/04/common-cold-combats-influen...
Some people treat "the immune system" like a muscle, where stress strengthens. Similar stressors can have cross-reactive effects, but unrelated ones do not.
This can go the other way too: people who have uncontrolled celiac disease (as in, they're still consuming gluten on a regular basis) can also have issues with avenin (a somewhat similar protein in oats) or even lactose. For a lot of folks those sensitivities disappear when they get their gluten consumption down.
I used to get injections to diminish my hay fever symptoms. I finally mostly grew out of hay fever around the age of forty, though I'm still allergic to horses and cats, if I have direct contact.
Don't those injections comprise increasing challenges to the immune system using the allergens themselves, to make it less prone to mount a histamine response (i.e. runny nose, itchy eyes)?