Hey,
Harvards University and Cambridge  University are one of the most prestigious institutions in the world and to be able to study here is an achievement in itself and is no less than a dream.
The enrollment for undergraduate programme in Medical in Harvards Medical School is based on various factors. You need to have an exceptionally brilliant academic record,extracurricular activities,research and community service in the field of health care. You need to have a baccalaureate in any disciple including Humanities or social sciences before applying for the medical programme. The MCAT( Medical College Admission Test) score is also important.
Now coming to Cambridge University, it offers two medicine courses- the standard course and Graduate course. If you don't have a degree,you can apply for Standard Course. Admission to Standard courses are through IB program or A levels.
For more details please follow the official website of Cambridge University:
https://www.undergraduate.study.cam.ac.uk/courses/medicine
Hope this helps.
Good luck.