By Nathalie Voit

The city of Philadelphia will reinstate its indoor mask mandate due to a recent surge in COVID-19 cases, the Philadelphia Department of Public Health announced in a statement on April 11.

Starting April 18, the city will require masks in all indoor public spaces, including schools, businesses, museums, restaurants, offices, and government buildings. Businesses and institutions can go mask-free if they require everyone on-site to be fully vaccinated and check vaccination status upon entry, the health department said.

Businesses will be given a one-week grace period to comply with the mandate and notify staff and patrons. However, beginning on Monday, the city will enforce the new requirements. Any businesses found to be breaching the mandate may be reported to the relevant health authorities, city officials said.

Philadelphia uses a series of metrics known as COVID-19 response levels to guide its public health strategy. The city’s public mandates are based on the appropriate response level. When cases go up, the city implements the relevant mitigation measures designed to protect residents. When cases go down, the city lifts those measures.

As of April 11, Philadelphia was averaging 142 new cases of COVID-19 per day. Additionally, cases increased by more than 50% over the past ten days, when the number of new cases averaged just 84 on April 1. The two criteria satisfy the city’s self-imposed benchmarks needed to enter into Level 2: Mask Precautions status.

The move makes Philadelphia the first major U.S. metropolis to reinstate its indoor mask mandate. The city had gone just six weeks without an indoor masking requirement. Officials had previously given the “all clear” on March 2.

“By implementing the mask mandate sooner rather than later, the Health Department hopes to keep the number of cases from skyrocketing, like we saw in December and January from the Omicron variant,” city officials said. “We know that masks work to protect us and our communities, so the sooner that Philadelphians start wearing them, the safer we all may be.”

It’s unclear when the mandate will end as it is tied to the city’s COVID response levels.