Contact tracing is clearly useful, but on it’s one does not change the basic reproduction numbers much. Look at South Korea which still has active infections despite active contact tracing and very successful social distancing.

Contact tracing COVID-19 is suplimental not a solution.

PS: As to my point, if you’re a grocery store employee in NYC you are likely to have been in contact with someone with COVID-19 in the last week. We can’t simply send all of them home, that’s the issue with contact tracing when a meaningful percentage of the population is infected. You need looser restrictions which reduces effectiveness.

“but not reduced it enough that contact tracing is likely viable”

For example, NYC has seemingly slowed the spread enough it’s possible to Test for and track new cases. But if you dig into their numbers 4,264 deaths are linked to COVID but where not tested prior to death. https://www1.nyc.gov/site/doh/covid/covid-19-data.page. They have little idea who’s currently infected and “ Due to delays in reporting, recent data are incomplete.”

Essentially they need a solid 2 weeks of minimal new cases. At which point they can start meaningful contract tracing, but contract tracing does not mean you can just get back to normal. Just slightly reduce the amount of isolation.

Remember, virus still doubles every 2-3 days under normal conditions. Without a vaccine or herd immunity, contact tracing alone does very little. It’s enough to reopen dental offices possibly hair salons, not schools.