family members, to notify co-workers. we actually shut down offices when they were in a situation with somebody infected. that became increasingly futile when the infection became so common. once it got out there, contact tracing was not the way to go. you have to isolate people and create a bubble for it to work. that's why we switched to measures like masking to keep things going. if a micron remains relatively infrequent, can you go back to contact tracing and try to get a handle on this, and i think that's a question we don't have an answer to yet. we'll have to see. >> that's a good point. there's also a travel ban on foreign travelers from southern africa, just put in place by the biden administration. they've faced quite a bit of criticism about this. i want to play for you how the surgeon general defended the response. >> travel restrictions we know will not permanently keep out a