Someone once told me that no one ever dies from leukemia, they said that death comes from pneumonia after the leukemia has made you too weak to resist it.
They are weakened by the underlying chronic disease and finished off by pneumonia. Also the treatment for many diseases will weaken the immune system leaving the patient open to opportunistic infections.
There are vaccinations available for Pneumococcal pneumonia caused by Streptococcus pneumoniae and anyone of Hillary’s age should have the vaccination.