A simple tool for comparing benefits and “costs” of COVID-19 lockdown exit strategies

Abstract

As several countries begin to exit various forms of COVID-19 “lockdown,” a simple epidemiological tool – Population Attributable Risk – can help guide decisions about specific exit policy options, by quantifying the proportion of “serious” (hospitalised) COVID-19 cases likely attributable to various combinations of individual risk factors at the population level, such as age alone, versus age combined with the presence of any chronic disease/risk factor. Using recent COVID-19 hospitalisation data from a large hospital network, and current Scottish population age structure and risk-factor prevalences, we show that the likely impact on adult hospitalisations would be very similar (an approximate halving, compared to full lockdown exit for all adults) for the most “moderate” and yet reasonably effective options for continued lockdown: continuing to restrict the social contacts of all persons over 65, compared to all persons over 50 with any chronic disease/risk factor. Other considerations are therefore of critical importance to this decision, such as the equity and acceptability of these two policy options, as well their likely economic impacts.