To get into medical school you need interesting and outstanding extracirriculars. If the way you want to set yourself apart is by doing some or alot of research, fine. Publications are NOT required to show that you've done alot of research, including at MSTPs, but they're a bonus. Make sure if you do this that you really get involved for more than just like 1 summer and that you really know what's going on. I've seen too many applicants who only seem to have done research to bolster their app and/or have no clue what was going on in a lab or even in a publication their name is on.
My point is: do something you enjoy, do it for a long time, and excel/lead at it. This doesn't have to be research.
PS: I had no publications and I was accepted MD/PhD and MD-only to a number of big name programs. This goes for the majority of my med school friends as well.