Hm, I might not entirely understand your question, but in my mind there is no connection between "millions" and "in." (Remember, "in" = "by" here.) The "in" ("by") is attached to the explanation of what affected the millions (of people). To demonstrate this, imagine the sentence were shorter:Originally Posted by oldboy
...and millions were affected. (But we don't know what affected the million.)
You would NOT say ...and millions were affected in. You would be left wondering "in what?"
There is no need for "in" until you introduce what was affecting the millions:
...and millions were affected in the poisoning.
I hope this makes sense. I wish I could think of a better explanation. Maybe someone else can add to this.