Again, you just don't allow them a visa until they demonstrate 21 days of residency outside of an outbreak region.
What about those who already have a visa?
Who is going to set up this quarantine/mechanism in every nation/airport outside of the outbreak region?
We have a difficult time with our southern boarder. Shall we post guards every 10 feet with orders to shoot anyone who approaches?
If we could get every nation on earth to cooperate, then travel bans might be a viable option. We can not even get Congress to cooperate. If this was as terrible a threat as it is being made in to do you think maybe Congress would come back from their two month vacation a little early and pass travel bans into law?
As far as I know travel bans haven't been taken off the table.
jtk
"A pessimist sees the difficulty in every opportunity; an optimist sees the opportunity in every difficulty."
- Sir Winston Churchill (1874-1965)