Our elected officials are faced with a difficult choice in determining how to reopen cities and states after a Covid-19 lockdown. On the one hand, it is not possible to maintain stay-at-home orders indefinitely. The economic consequences would be catastrophic. But removing all restrictions can result in massive increases in sickness and death (as we are now beginning to see in some states). So how can a balance be struck that avoids business collapse while minimizing health problems?
That is the subject of an article published on Medium called “As Cities Move Toward Reopening, How to Manage Risks,” by Darria Long and David Katz. Long and Katz provide a framework for deciding who should be permitted to return to work during the pandemic. The framework also provides a way of talking about pandemic safety more broadly.
Their advice comes in two parts: determining a given person’s degree of risk from Covid-19, and determining the viral dose associated with various activities. Taken together, this provides a framework for saying “people in category X should avoid activity Y”.
Determining a person’s risk from a Covid infection. The basic approach taken by Long and Katz is laid out in a 3 by 3 table, called a “risk-stratification matrix”. On the vertical axis is “Health-related risk tiers”: “High” is for people with worrisome pre-existing conditions, “Intermediate” is for generally healthy people, and “Low” is for healthy people with no chronic conditions. On the horizontal axis is “Age-related Risk Tiers”, with “High” for those who are 70+ years old, “Intermediate” for 50-69, and “Low” for those under 50.
Those who are “High” on both scales require sheltering in place. Those who are low on both can “return to the workplace” as long as they “manage activities to minimize exposure dose”. The others require intermediate levels of care in minimizing exposure.
Here is the Risk-stratification Matrix from the article:
Minimizing viral dose. “Dose” is the other half of the strategy. Minor exposure to the virus will be handled by almost anyone’s immune system, but large doses of virus need to be avoided (especially by those in the high-risk categories). Long and Katz rate risk based on the “four Ds”: high Density of people (Long and Katz include airflow as part of this factor), high Degree of activity, long Duration of the encounter, and limited Distance between people.
When these four factors are all present, that’s a “high dose” setting. When none are present, that’s “low dose”.
Long and Katz stop short of saying exactly how this framework should be applied by policymakers, but at lease they provide a language for describing the risk categories and potential dosages. Although the article specifically addresses returning to work, the same factors and framework can be applied to other situations (including the issues surrounding reopening at Kendal).
As residents at Kendal, we are mostly in the “high” age-related risk tier. Many of us are also in the “intermediate” or “high” health-related risk tier. That means that we must studiously avoid “high dose” situations, and that is in essence what our current restrictions are all about.