RADNOR, Pa. (CBS) – Seven cases of whooping cough have been confirmed at Radnor High School since March 20.

In a letter to parents, the district said that of the seven cases, six of the students were vaccinated.

The Pennsylvania Department of Health recommends that all students at Radnor High School be observed for symptoms of whooping cough and report any symptoms to their pediatrician immediately.

The school district says in the letter, “Efforts have been intensified in the daily cleaning and disinfecting of rooms and surfaces.”