When did this science become known. SARS-CoV-2 is Covid and this knowledge was known over a year ago...So they did not follow the science earlier...now that people cant fly over the holidays and are blameing Brandon they decide to pull the science card and move to 5 days CDC: The change is motivated by science demonstrating that the majority of SARS-CoV-2 transmission occurs early in the course of illness, generally in the 1-2 days prior to onset of symptoms and the 2-3 days after.