“No one came in and no one came out. Schools were closed and there were no public gatherings. We came up with the term ‘protective sequestration’, where a defined and healthy group of people are shielded from the risk of infection from outsiders.”
Humans now have the ability to travel much greater distances at much greater speeds. That makes it a lot harder to sequester large groups of people. The long borders to the north and south make it nearly impossible to completely shut down US inflow.
Most people travel through authorized checkpoints, and such authorized travel can be easily stopped, delayed, or restricted. That would be likely to be effective at greatly reducing most, though some desperate people could still try to get through by other means. But at least it'll stop the casual travellers and those not willing to take great risks to get through.
"The long borders to the north and south make it nearly impossible to completely shut down US inflow."
But one does not need to completely shut down US inflow to make a significant difference or slow down the progress of the pandemic to give more time for governments and health agencies to react.
It's likely that governments will be slow to react, and not take the problem seriously enough until it becomes too big to stop. Fast, early, decisive action is critical in containing such outbreaks.
That said, I have read health experts say that shutting down borders won't be effective at stopping pandemics.
The most effective thing (once this pandemic is over) is focusing on prevention of future pandemics, through much greater investment in public health, poverty-reduction measures, reduction of factory farming, research, and education. It's the lack of commitment to such measures that lead to greater risks of pandemics and lack of effectiveness against them.
So what/why are you arguing?
Former CDC Chief: https://www.foxnews.com/opinion/cdc-chief-why-i-dont-support...
World Economic Forum Executive Director: https://www.weforum.org/agenda/2014/11/why-travel-bans-will-...