Published research is what matters. Ideally in the field you are interested in, but any published work will do. The research requirement is really exaggerated, though. It's more of a plus than a requirement, except at the few programs that want to train physician scientists. Your USMLE score is by far more important.
There are many MS1 summer fellowships offered between the summer of MS1 and 2. You should try to sign up for one of those as soon as you can and be as productive that summer as possible. You'll probably get your name on something by the end of the summer.