Shielding individuals at high risk of COVID-19: A micro-simulation study

Abstract

Background: One proposed intervention for mitigating COVID-19 epidemics, particularly in low-income and crisis-affected settings, is to physically isolate individuals at high risk of severe disease and death. This intervention, known as ‘shielding’, could be implemented in various ways. If shielding is imperfect, any introduction of infections within the shielding group could cause substantial mortality and negate the intervention’s benefits. We explored the effectiveness of shielding under various modalities of implementation and considered mitigation measures to reduce possible harms. Methods: We used an individual-based model to simulate a COVID-19 epidemic in a population where a fraction above a given age are relocated to shielding residences. We set our simulation with the context of an internally displaced persons’ camp in Somaliland, for which we had previously collected data on demographics and social mixing patterns. We compared an unmitigated epidemic with a shielding intervention accompanied by various risk-mitigating measures. We explored the impact of parameters such as residence size, reduction in contacts, basic reproduction number, and prior immunity in the population. Results: Shielded residences are likely to be breached with infection during the outbreak. Nonetheless, shielding can be effective in preventing COVID-19 infections in the shielded population. The effectiveness of shielding is mostly affected by the size of the shielded residence, and by the degree by which contacts with the outside world are reduced. Reductions in contacts between shielded individuals are only effective in larger shielded residences. In epidemics with a lower reproduction number, the effectiveness of shielding could be negative. Conclusions: Shielding could be an effective method to protect the most at-risk individuals. It should be considered where other measures cannot easily be implemented, but with attention to the epidemiological situation. Shielding should only be implemented through small to medium-sized shielding residences, with appropriate mitigation measures to prevent subsequent spread.