[CliffordK (OP)]

I was reading about resistance to the drugs Amantadine and Rimantadine, as well as some of the newer antivirals for Influenza.

I was surprised to read that antiviral drug resistance for at least these two drugs is very high since I didn't think they were commonly prescribed. 

It may be virus strain specific, as on an annual basis, essentially a couple of clonal strains quickly spread around the globe.  So, if the virus has picked up the resistance gene, it then spreads everywhere.

It is interesting that several zoonotic derived influenza viruses including H1N1 (Swine Flu) carried antiviral resistance, despite presumably only being infectious to humans for a relatively short period.  Was the resistance developed in livestock?  Or early hospital treatments?