BOL! My mother, who was 0- and never had any flu and seldom had colds was a teacher for most of her adult life. She and my O-negative sibling seldom had allergies or colds.
She was a teacher back in the 1940-s & for 60+ years. With the exception of an emergency gyn surgery when she was 40 something, she never had allergies nor sinus problems like my Dad and I did. She did have adult onset arthritis in her hands after turning 80.
My 85 year old mother was perfectly healthy until she got covid. Until that point, she was seemingly invulnerable other than the usual slow decline from getting older.
However, it took her almost a year to recover from covid and she ended up with a stone in her pancreas ducts. That nearly finished her.