Research pubs on your CV can help you but are not needed. If you are an MS2 trying to strengthen your application, there is more bang for your buck if you spend the time you would have spent on research, and apply it to reading, studying, and preparing for your step scores and dedicating your time to working your butt off during your third year clerkships so that you get good evaluations and high shelf exam scores (and excellent clerkship final grades). If the opportunity falls in your lap to write up a case report or present a medically challenging case at the ASA or other meeting, certainly jump on that, but doing a huge and time consuming research project that takes away study time can be detrimental. Also recall that it can take years to do research and the likelihood of getting a project completed, presented at meetings, and published by the time you need it "on your CV" is low.
In summary, a candidate with a step score of >250 and no research will likely get far more invites than the same candidate who has a 220 step score and a research publication. Obviously, if you can accomplish both, you will be in the rare situation where you will likely be invited to interview at >90% of programs you apply to.
Very few things have the ability to increase your number of invites like a high USMLE score and very few things can lower the number of invites you get like a dismal step score. I believe that too much emphasis is placed on the exam, but it is what it is and with the increasing uselessness of the dean's letter, the lack of class rank at more and more schools, and the uselessness of most letters of rec, it has become one of the only ways to screen potential applicants.