>So let's start testing aggressively for antibodies. Until we get that number, I'm all for extreme caution.

There is no Antibody/serological/immunity test yet. Biologically it is harder even that a vaccine... Test WILL be intensive/invasive (think blood, not mucus), much more so than a simple test for presence/absence of a particular virus.

https://www.reuters.com/article/us-health-coronavirus-immune...

Important though