This is all highly experimental.
What if you got back to earth and the inoculation wore off unexpectedly during your big reunion?
Boom, and there's an arc for season 3.
Very Xindi-like. A new race in the alpha quadrant: the Newt-toids. I bet Harry Kim's character would be better as a newt anyway. Or hey, maybe they accidentally slingshot around the sun on the way back to earth, and then they go back in time to earth in its early stages. And then we learn the human race actually evolved from the crew of Voyager. It's the circle of life. I can hear Elton John right now...