mr bill -
Very good question. Just what exactly does "immunocompromised" really mean?
Going to the National Cancer Institute's Dictionary of Cancer Terms https://www.cancer.gov/publications/dictionaries/cancer-terms/
and searching the word yields:"Having a weakened immune system. People who are immunocompromised have a reduced ability to fight infections and other diseases. This may be caused by certain diseases or conditions, such as AIDS, cancer, diabetes, malnutrition, and certain genetic disorders. It may also be caused by certain medicines or treatments, such as anticancer drugs, radiation therapy, and stem cell or organ transplant. Also called immunosuppressed."
A definition which, to my layman's ears, seems a bit unspecific (for example, what does "reduced ability" mean?), at least in terms of practical application to a particular situation.
But maybe the lack of specificity is intentional?