[mlyle]

50-66% is most likely, and perhaps less. Estimates of R0 are mostly in the range of 2.0-2.5.

50% would lower a 2.0 R0 to 1.0. 66% would lower a 2.5 R0 to 1.0. And this ignores that we may have permanently changed behaviors (e.g. handshakes) that facilitate spread, so we may not even need this fraction to curb tramission.

New York City is presently somewhere past 23%, so that's a big chunk of the way to a 1.0 Rt without controls.