The gray zone: How not imposing a strict lockdown at the beginning of a pandemic can cost many lives

The public debate on the effectiveness of lockdown measures is far from being settled. We estimate the impact of not having implemented a strict lockdown in the Bergamo province, during the first wave of the COVID-19 pandemic, despite observing an infection rate in this area similar to the one observed in nearby municipalities where a strict lockdown was instead promptly implemented. We estimate the causal effect of this policy decision on daily excess mortality using the synthetic control method (SCM). We find that about two-thirds of the reported deaths could have been avoided had the Italian government declared a Red Zone in the Bergamo province. We also clarify that, in this context, SCM and difference-in-differences implicitly restrict effect heterogeneity. We provide a way to empirically assess the credibility of this assumption in our setting. •Causal impact on excess deaths of not locking down the Bergamo province in 2020.•A lockdown would have prevented up to two-thirds of deaths due to COVID-19.•The results show irreversible costs of not promptly enforcing a strict lockdown.•It is proven that estimating the pandemic’s effects requires additional assumptions.