US does not provide any MBBS programmes like that of India. The candidates do a graduation in Biology and then apply for residency in Harvard. The residency is equivalent to MD/MS in India. For residency in USA, students need to give USMLE which is a three step examination. The highest scoring international students gets to choose the top one like John Hopkins, Harvard etc. Also you need to have a strong Cv with research background, and recommmendation letters.

Hey,
Well Harvards University is not just an institution,it's a dream. Only the best get to study here. The infrastructure,the exposure and the sense of validation that it offers is unparalleled.
Harvard University does not conduct any specific entrance test but your overall academic record plays an important role in determining your result.
The committee on admission evaluates applicants based on several,including the following:
Academic records,Applicant essays,MCAT Scores,Letter of evaluation,Extracurricular Activities,Life Experiences,Experience in the health field.
Harvards School of Medicine doesnot enroll for undergraduate degree. You must complete your graduation.Remeber it doesnot give preference to any applicant who has majored im Science over others who have majored in  other disciplines. But if you enroll in a medical school then you are not eligible to apply for Havard Medical School.
You may go through the official link of Harvard Medical School for further in depth information:
https://meded.hms.harvard.edu/admissions-selection-factors
Hope this helps.
Good luck.

Hello,
https://meded.hms.harvard.edu/admissions-before-you-apply
Given above the official website link for eligibilty criteria
Everything is given in details.Better you refer this link as many sub points are also given.
Hope I helped you.All the best for future endeavour!!!