In the US, we have medical interns. They have completed their classroom studies, but not yet started residencies. They typically work as poorly paid interns for 18 months(?), doing quick rotations through the various specialties, before moving on to their residencies.

They are paid poorly. I think the base rate is about $35k/year. But, at this point, they are still effectively students. I believe the MD is granted upon completion of the internship (or maybe they have the MD, but not the license to practice, I can never remember).

Ugh. Internist is not a synonym for intern, unpaid or otherwise. An 'internist' is a sub-specialty of fully-licensed medical doctor, as in 'internal medicine'. It's equivalent to a pediatrician except specifically focused on care for adult patients, in contrast to a 'family practice' or 'general practice' doctor, who focuses on both adult and pediatric patients.