Question: Is there a threshold for community transmission that schools should consider for closing/reopening?

Answer: CDC released its updated school return guidance late last week. I’ve copied a few key portions below for ease of reference (Table 1). CDC suggests school closing only in the context of:

• substantial, uncontrolled [community] transmission — “If there is substantial, uncontrolled transmission, schools should work closely with local health officials to make decisions on whether to maintain school operations.”; and
• someone in the school tests positive — “If someone within the school community (e.g., student, teacher, staff) tested positive for SARS-CoV-2, assessing the level of risk is important to determine if, when, and for how long part or all of a school should be closed.”

With regard to “substantial, uncontrolled transmission,” CDC describes levels of community transmission here (Table 2), but these levels do not include specific numeric thresholds. Within its guidance, CDC suggests that school systems use “indicators such as healthcare capacity (e.g., staffing, ICU bed occupancy), changes in newly identified COVID-19 cases, and percentage of people testing positive for SARS-CoV-2 infections in the community might be useful to determine whether to maintain or modify school operations.” This is moderately helpful, but for me, the challenge is that without numeric thresholds, it’s much harder for us to understand school return decisions; the criteria are not transparent. For example, what does “substantial, controlled transmission” look like? Would a given leader define their community’s substantial transmission levels “controlled” or “uncontrolled” and how would that description be weighted based on political, economic, health, and welfare concerns (among others)?

If we were to consider as numeric thresholds/benchmarks the indicators CDC suggested for phased reopening (Table 3), then indicators of “sustained, controlled transmission” would include downward trajectory of new cases; downward trajectory of % tests positive; tests positivity at </=20%; and tests returned within 4 days. Other groups, like Resolve to Save Lives and the Pandemic Response Network have drafted pandemic severity/alert criteria (see here). Interestingly, they suggest that in-person learning be curtailed in the context of both “substantial, uncontrolled transmission” and “substantial, controlled transmission” (e..g “high alert” and “moderate alert” respectively). With regard to this component of the debate — whether to have in-person learning at “substantial, controlled transmission” — I don’t know which is the right answer.

Table 1. CDC Guidelines for Making Decisions about School Operations

Table 2. Levels of Community Transmission (from CDC)

Table 3. Gating Criteria for Phased Reopening (from CDC)