Bioactivity is the effect of any given agent upon a living organism.  For example, vaccine use.  A new substance being introduced to the existing environment and resulting in a change. 

Today I happened to spend some time with Jimmy.  Born and raised locally, embarrassed to find himself in use of a cardboard sign and in the market for Pall Mall 100ʻs.  He introduced himself to me.  I introduced myself to him.  We talked about life and colors and his accident.  He smiled frequently.  I felt brightness.  Some small part of me was changed by having Jimmy introduced into my life and maybe some small part of him by me.

The world needs change.  Our environments need vaccines.  Maybe that's you and me.  And maybe it's just an introduction away.