The mandate, which will run from Jan. 3-13, is aimed at reducing the spread of respiratory illnesses after a holiday season likely filled with more social gatherings and increased exposure, the school district said in a statement on Thursday.
Philadelphia is among state and local agencies around the United States rolling out mask mandates or recommendations this month to fight a new surge in virus cases, which is expected to grow as Americans travel and socialize around the winter holidays.
Health experts say the U.S. healthcare system is under strain because of a "tridemic" caused by Covid-19, influenza and respiratory syncytial virus (RSV). White House Covid-19 response coordinator Ashish Jha said on Thursday the country was probably experiencing its worst flu season in a decade.
The White House on Thursday announced that families could again order free Covid-19 tests from the government website COVIDTests.gov due to the nationwide rise in cases.
But nearly three years into the Covid-19 pandemic, fewer localities are rushing to enforce strict mandates than in previous years. There is debate over the mandates' efficacy, as months of stringent public health rules early in the pandemic exacerbated the public's Covid fatigue and stoked political controversy.
California's public health department on Thursday told Reuters it was urging people to wear masks, but stopping short of requiring them.
Dr. John Swartzberg, an infectious disease expert at the University of California, Berkeley, said the triple whammy of the respiratory diseases is already straining hospitals and, reminiscent of the pandemic's earlier days, leading facilities to cancel elective procedures.
While the political will to impose mask mandates may have waned, covering one's face remains the best way to avoid getting sick - and infecting others.
"If you don't want to get sick and you don't want to go to the hospital and you don't want to die of Covid or influenza, or if a very young child, RSV, then you should be wearing a mask indoors in a public place," Swartzberg said.
Purchase College, part of the State University of New York, announced on Tuesday that indoor masking was again required, citing a level of "high transmission" of the virus locally.
The Sacramento Unified School District in California said on Dec. 5 that if community transmission returned to high levels, masks would be required indoors.
Los Angeles County Public Health Director Barbara Ferrer said the county would impose an indoor mask mandate if the community-level spread became "high" by the U.S. Centers for Disease Control and Prevention's standards, which look at new Covid-19 hospitalizations and cases in relation to a total population.
New York City's Health Commissioner last week "strongly urged" New Yorkers to wear masks in public indoor settings and crowded outdoor places, even though community transmission there is already "high" by the CDC's standards.