Less than two weeks after the Philadelphia School District reopened for some in-person instruction, it is temporarily closing a school because of COVID-19 cases.

The school, Mayfair Elementary, will close through April 1; it and 52 other buildings reopened to some prekindergarten through second-grade students March 8. The closure is to “help stem the spread of the virus,” principal Guy Lowery wrote in a letter to the school community obtained by The Inquirer. “Students and staff may not return to our school building at this time.”

Classes will continue virtually, officials said.

It’s unclear how many total cases have been reported at the school. District officials have not disclosed the number of positive cases at Mayfair or other schools, but a staffer at the school said Mayfair employees have been notified of at least five cases.

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Only staffers and some second-grade students had been inside the Mayfair building; because of overcrowded conditions at the school, Mayfair’s kindergartners and first graders typically attend school at nearby Austin Meehan Middle School, which has not reopened.

Over 2,100 students in grades K-8 are enrolled at the school, one of the city’s largest. Only about 30 students had been inside Mayfair since March 8.

Though the building can reopen April 1, students will not be back inside until April 5, when they’re scheduled to return from spring break.

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Monica Lewis, a school system spokesperson, said student and staff health is the district’s highest priority. She said Mayfair would be sanitized and deeply cleaned prior to reoccupancy.

Jerry Jordan, president of the Philadelphia Federation of Teachers, said he was alarmed to hear from some members that efforts to trace COVID-19 cases have been delayed.

“This is unacceptable,” said Jordan. “The district must immediately address their notification and tracing protocol and must provide a standardized reporting mechanism, including a publicly accessible dashboard.”

Jordan also said the district needs to “double down” efforts to ensure mask compliance.

In total, 98 Philadelphia public schools have reopened for some in-person education after being fully remote for a year due to COVID-19. Thirty-five more schools are scheduled to open for in-person learning for some prekindergarten through second graders Monday.