When playing as Carlos in the Hospital 4F, go to the unlocked Sickroom and look at the corner where the movable cabinet is located. Remember where it is. Read the note on the dead doctor's hands in that room. Use the Sickroom Key on the next room over. In that room, push the cabinet in the opposite corner of where the cabinet in the previous room was found. For example, if the first cabinet is in the upper left corner of the first sickroom, than push the second cabinet into upper right corner of the second sickroom. A painting in the room will slide, revealing a machine holding the vaccine base. Enter the numbers that were on the dead doctor's note in order to obtain the vaccine base.