Sick people and healthy people can catch flu ~ swine flu, or old-fashioned flu cooked up over at the neighbors.
I think you are confounding "catch" with "kill". Healthy people may well not have secondary conditions that are assisted in killing us if we catch flu.
Forgive my shorthand, then. By virus being “not easily transmitted to healthy humans” I obviously meant people not being seriously affected by such virus to the point of disease... in the same meaning as “catching a virus” usually means having already developed the symptoms of the disease rather than having copious quantities of virus deposited on the hands and washing them away with soap.
Obviously, “healthy humans” are the ones who at the time don’t have weakened immune system - for many reasons, including stress or other diseases - that makes them more susceptible to be affected by virus.