Three students and one staff member of Pompton Lakes High School tested positive, Mayor Michael Serra said in a Facebook post.
This brings the total number of cases in Pompton Lakes to 255, Serra said.
"The student cases seem to be related to an outside of school event where all the children were together," the mayor said. "All individuals are isolating at home and, thankfully, all feeling fine."
The students' exposure likely occurred over Labor Day Weekend, according to Superintendent Paul Amoroso.
Contact tracing is under way.
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