The Philadelphia School District announced Friday it would allow those who have been exposed to COVID-19 but show no symptoms to stay in school if they mask for 10 days, isolate, and test for the virus if they begin to feel sick.

The so-called “mask to stay” policy comes as case counts are on the rise in Philadelphia, and is aimed at eliminating quarantines to “support in-school learning and reduce the strain on classroom coverage,” spokesperson Monica Lewis said in a statement.

Though no Philadelphia schools are closed because of COVID cases, some schools are experiencing “active clusters of positive cases across multiple cohorts,” she said. At those schools, all students and staff must mask for 10 days.

Students at those schools who refuse to mask after being identified in a cohort must quarantine at home for 10 days, or quarantine at home, then test between days five and seven, and return on day eight with a negative test.

In other district schools, masks remain optional. Under federal rules, students and staff in Head Start programs must continue to mask.