Performance measures

For each of the protocols we consider three different performance metrics. Total cluster size is the number of students who are ultimately infected in class (or in both classes in the high school), including the index case. Total disrupted is the total number of students who are either asked to isolate or are tested. A student is included if they became symptomatic and had to isolate, if they were a member of a group that was asked to isolate, or when their class was asked to isolate (or be tested).

We did not explicitly simulate the number of new clusters that a cluster seeds through out-of-class social contacts (siblings, parents, teacher-teacher contact, after-school activities and so on). A measure of the risk of such “bridging” interactions is asymptomatic student-days, the total number of student-days when students are infectious, but are not isolating outside of the classroom. We assume that all symptomatic students are isolating outside the classroom, but whether asymptomatic students are depends on student behaviour, which is influenced by public health guidelines. We use the term policy to indicate the guidelines for student isolation outside the classroom, and its subsequent effect on student behaviour, (whereas we use protocols to refer to what happens in the classroom, as before.) Under a lax policy we assume that asymptomatic or presymptomatic students are not told to isolate (regardless of whether their group or class is shut down), and the number of asymptomatic student-days is just the total number of student-days of infectiousness without symptoms. Under a strict policy we assume that when a group or class is shut down all students in the group are told to isolate until they recover or receive a negative test result. So the asymptomatic student-days under this policy is the total number of days students are infectious but asymptomatic before their group or class is shut down.