it's been our experience w/southwest (and lots of experience at that) that they do NOT clean the entire plane, it is up to the passenger to sanitize their area and any other area they think they may come in contact with (i've got it down to a science!)... they allow allergy passengers to pre-board to give them time to do that... they also strongly recommend getting the first flight of the morning as those planes have been cleaned/vacuumed/sanitized/etc...