You're confusing a virus with a bacteria (Score 0)

If I recall my virology class, a virus usually randomly mutates, causing it's receptors to take on a different biochemical arrangement, which is what leads to resistance to antibodies. Most inoculations against flu are a weakened version of a virus, which causes an immune response. Using an enzymatic agent against a virus seems a novel approach.

Bacteria are constantly going through many generations and exposure to various drugs can cause many mutations as a response. Newly mutated bacteria that can survive the drug are selected out of the others, leading to a resistant version.