Critical weaknesses in shielding strategies for COVID-19

TL;DR

This study uses a stochastic model to evaluate the strategy of shielding vulnerable populations during COVID-19, concluding it would likely overwhelm healthcare systems and result in many avoidable deaths, thus being an ineffective approach.

Contribution

The paper provides a quantitative analysis showing the impracticality of shielding strategies for COVID-19 using a stochastic SEIR model, highlighting their limitations.

Findings

Shielding vulnerable populations would have overwhelmed hospitals.

A 20% reduction in shielding effectiveness could increase deaths by over 150%.

Shielding is unlikely to be a viable strategy for future pandemics.

Abstract

The COVID-19 pandemic, caused by the coronavirus SARS-CoV-2, has led to a wide range of non-pharmaceutical interventions being implemented around the world to curb transmission. However, the economic and social costs of some of these measures, especially lockdowns, has been high. An alternative and widely discussed public health strategy for the COVID-19 pandemic would have been to 'shield' those most vulnerable to COVID-19 (minimising their contacts with others), while allowing infection to spread among lower risk individuals with the aim of reaching herd immunity. Here we retrospectively explore the effectiveness of this strategy using a stochastic SEIR framework, showing that even under the unrealistic assumption of perfect shielding, hospitals would have been rapidly overwhelmed with many avoidable deaths among lower risk individuals. Crucially, even a small (20%) reduction in the effectiveness of shielding would have likely led to a large increase (>150%) in the number of deaths compared to perfect shielding. Our findings demonstrate that shielding the vulnerable while allowing infections to spread among the wider population would not have been a viable public health strategy for COVID-19 and is unlikely to be effective for future pandemics.