  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.
