It's not important at all.
For a simple reason. The USMLE question takes months and years of filtering, peer reviewing, editing, auditing, and approval until it makes its way to the real bank. Therefore, it's impossible for you to see a question in the exam about an article or research that has been recently written.
One or two years back "big bang" research is usually found in updated USMLE Books and references and so you don't need to bother about journals.
Besides, who has the time to read all those journals? Are you kidding me