I'm torn on that one. I liked the show and wanted to see more, but they sort of wrapped things up by reuniting the woman (can't remember her name) with her long lost son, which seemed to be a big part of the plot. As for Tom, I liked him a lot and would have loved to see more, but with how they ended it I got the impression that he went back on the plane and then kicked ass at the virus HQ. Not the most satisfactory of endings, but I can live with it.
Or as the saying goes that I got from a Chinese fortune cookie: "What the mind does not allow the heart does not grieve".
I felt like it was a pretty clean closing. Yes Tom stowed away on the plane to the pharmacy place but Abby and Peter are reunited plus they have a working vaccine to ensure the virus does not make any comebacks. All things considered it is both a good place to leave off and also gives enough "hooks" for the story to be picked up at a future date.