Take Los Angeles, for example, the second most populous city in the US. Health officials say LA County’s high Covid-19 community level means a universal indoor masking mandate could be enacted as soon as this week. While daily reported cases have leveled off, with about 6,700 new cases daily, Department of Public Health Director Barbara Ferrer said last week that the community level must decline back to “medium” by July 28 to avoid an indoor mask requirement occurring on July 29.

And it’s not just LA that’s reacting to rising case numbers and hospitalizations. The share of the United States population that lives in a county with a “high Covid-19 Community Level,” where the US Centers for Disease Control and Prevention recommends universal indoor masking, has doubled over the past two weeks. And as Americans have switched to more rapid at-home tests, official case counts reflect just a fraction of the true disease burden.

That’s why there’s renewed discussion of indoor masking, with Boston, for example, issuing a new mask advisory earlier this month. But a lot depends on local politics, and the merits of such measures — especially mandates — remains a matter of debate.