Philadelphia has fewer COVID-19 cases than the surrounding counties despite having lower vaccination rates—and the main reason could be the mask mandate, writes Jason Laughlin and Aseem Shukla for The Philadelphia Inquirer.

At 56.3 percent of the fully vaccinated population, the city trails all of its collar counties.

Chester County is currently at 61.3 percent, Montgomery County is at 62.2, Bucks County is at 64.8, and Delaware County has the highest vaccination rate at 65.6 percent.

Even so, Philadelphia has a lower percentage of its population infected by COVID-19 than each of those counties. The Philadelphia Department of Public Health has a theory on why.

“The only difference I see is the mask mandate,” said Cheryl Bettigole, Philadelphia’s acting health commissioner. “It’s hard to see what the difference is otherwise.”

In August, the city reinstated the indoor mask mandate when cases surged once again driven by the delta variant. No other parts of the state have a similar mandate.

“Step on the other side of City Avenue and masks disappear, so we definitely think that Philadelphians are better masked,” said James Garrow, a health department spokesperson.

Read more about the issue and the mask mandate in the city in The Philadelphia Inquirer.