La Salle University will return to in-person learning Monday, after a rapid spread of the coronavirus spurred a week of virtual classes.

Officials at the 4,624-student university said Friday they had tested more than 625 people and conducted “significant” contact tracing after the number of active cases rose from four to 48 over the course of last weekend.

As of Friday, the university’s COVID dashboard shows 96 estimated current cases, and another 18 symptomatic cases that are pending testing.

“We have determined the spread is not only traceable, but manageable — particularly when considering our community’s high vaccination rate,” Tim O’Shaughnessy, the university’s interim president, said in a message to the community. “We are confident it is safe to return to in-person learning.”

Almost all transmission has been traced to large social gatherings off campus, and “classroom transmission has been nearly nonexistent, with only two such potential occurrences,” O’Shaughnessy said. He added that most of the people who have tested positive have had mild symptoms, and “many continued to attend class and other functions, believing their symptoms were related to seasonal allergies.”

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The university is adding staff to bolster its testing and contact tracing programs, O’Shaughnessy said.

As with other colleges in Philadelphia, La Salle students, faculty, and staff are required to be vaccinated or submit to regular testing — a measure the university put in place this summer, along with masking.

O’Shaughnessy said Friday more than 85% of the university community was fully vaccinated. He noted that it was the last day for those who are still unvaccinated to receive a first dose and remain compliant with the city requirement, and encouraged them to find a nearby clinic.

Though in-person classes will return, “this week serves as a reminder of our semester’s fragility,” he said. “Even with a strong vaccination rate and the extensive health protocols that are in place, we remain vulnerable to this virus.”