To major in Medical Microbiology and Immunology, all you need to do is BIOS1201/1101, CHEM1101/1121, One of MATH1031 OR 1041, and MICR2201, 2011, 3041, 3051, and one of 3061 or 3081. Just check the handbook for this major to be sure.
Right now, all you need to worry about is to enrol in BIOS...