Francis Suarez, a Republican, is mayor of Miami and vice president of the U.S. Conference of Mayors. Vin Gupta is an assistant professor of health metrics sciences and pulmonary/critical care medicine at the University of Washington Medical Center.

We are at war with a silent and ruthless enemy, and mask mandates are among our best weapons to win the fight. But they have to have teeth to work.

Facing a global pandemic with flu season on the near horizon, our nation’s governors and mayors must quickly align common sense with the common good. That means balancing personal liberty with the clear and present public health danger presented by the spread of covid-19. We can no longer afford to be confused by false choices and false information.

In short, warnings to anyone not wearing a mask need to be backed up with the threat of fines and, for chronic offenders, even arrest. There is no time to waste on half-measures.

Florida’s Miami-Dade County has already recorded more than 107,000 covid-19 cases and 1,400 deaths from the disease. So, starting this month in the city of Miami, where one of us (Suarez) is mayor, residents now risk a legal penalty if they venture into public without a face mask. The city has assigned at least 39 police officers to make sure that residents are following the city’s mandatory mask ordinance. Offenders will be warned but, if they refuse to comply, they will be fined. The first offense will cost $100 and the second another $100. With a third — God forbid — the offender will be arrested.

Importantly, this is about education and enforcement: The effort isn’t just about mandating masks in public settings (and ensuring they are broadly available to anyone, regardless of income status) but explaining why a mandate is necessary, and then ensuring adequate enforcement. And education comes first. By now, the need for masks shouldn’t come as a surprise to anyone in Miami — signage and awareness campaigns have been ongoing to ensure residents are informed and engaged.

Critics will likely assail this policy as government overreach at its worst. Moreover, they will repeat a widespread urban myth: that mask requirements simply haven’t worked. The truth, however, is that mask orders require continuous education and universal enforcement to be successful, and it is incomplete and incoherent mask orders that have had mixed or limited outcomes.

Only 6 in 10 Americans report wearing a mask all the time in public, with broad geographic variation. In Washington state, a recent survey suggested only 4 in 10 residents comply with recommendations; this lack of cooperation is cited as a key factor in a recent outbreak in Yakima, Wash.

We know from a compelling body of scientific literature that thick, well-fitting cloth masks can dramatically reduce covid-19 transmission. We also know that universality is key: Any benefit requires consensus and broad cooperation. That’s one reason Hong Kong was largely spared the worst of the pandemic despite being a puddle jump from Wuhan: Its citizens embrace mask-wearing at near universal rates. It’s also why the Institute for Health Metrics and Evaluation estimates that nearly 100,000 American lives could be saved between now and the new year if everyone wore a mask in public settings.

But the challenge of compliance remains. The simple truth is that humans generally respond to the threat of a fine and modify their behavior accordingly. That’s why busy downtowns use fines to promote adherence to parking rules — you’re far less likely to do what’s convenient (park illegally) if you know you’ll be on the hook for a $50 fine. It’s just human nature.

Success hinges on clear and consistent enforcement that everyone understands. And doing that work can also take pressure off ordinary people who are simply trying to do the right thing. In recent weeks, individuals have faced injury and even death for valiant attempts to promote adherence to mask rules among their fellow Americans. In Michigan this month, a 77-year-old man was allegedly stabbed by someone three decades younger after an argument over a mask. That followed the disturbing report in May of a security guard who was shot and killed at a Family Dollar store, also in Michigan, after confronting non-masked patrons.

The nation should follow Miami’s example. Governors have the ability to institute a mandatory mask policy with enforcement, and mayors have the responsibility to ensure effective implementation. We cannot afford to wait.

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