The first "two years" of medical school are the basic sciences and the second two years are clinical rotations. The first "two years" involve actual attendance at the school of your choice and the "two years" can vary in length. Some schools do last the entire calendar years due to breaks/vacations/holidays while some schools do not take these extended breaks and are completed in fewer calendar months. After you complete the Basic Science portion you begin doing clinical rotations at the hospitals affiliated with your school. So, in the case of SJSM, you would do 16 months on the island and then return to the US to do the clinicals.
Life is sexually transmitted.