Have your vitamin D3 tested.
I’ve never gotten the flu, never gotten a flu shot but always had head colds (and allergies) turn into pneumonia.
But not since I started taking the d3.
I have been tested, I am low normal D3.
We lived in a small Texas down in the 60’s and 70’s. They had a policy that said if a high school student had not missed a day and had at least a C average, they didn’t have to take the finals at the end of the school year.
Guess what happened? The students went to school sick and passed it to everyone in the high school who took it home to their younger siblings........
you get the picture. The entire town ended up sick with the flu.
We moved from there in 1979 and I was glad to leave.
The sickest I have ever been in my life I caught while on jury duty. Viral bronchial pneumonia, I thought I was dying.