adherent to these recommendations. so we're really saying if you're going to only isolate a certain period of time, we want to make sure you're doing so when you're maximally infectious those first five days, and please protect your others by wearing a mask those last five days. >> director walensky, good morning. this is jon lemire. i want to push you further on this. the uk moved its isolation from ten days to seven. what's the reasoning going all the way to five? and how do you address the concerns of someone who knows their coworker tested positive just five days before, no longer -- does not have to show a negative test to go back to work, might be wearing a mask, but surely understandable why that person was anxious sitting next to someone who is positive? >> two questions there. one is the uk guidance -- the uk is using antigen tests in a different way. they are testing very frequently with their antigen tests. they are actually picking up