How long does a lockdown need to be?

TL;DR

Effective epidemic control requires combining social distancing with early detection and isolation, enabling shorter lockdowns and better epidemic peak reduction, as demonstrated through simulations in Italy.

Contribution

This paper introduces a combined strategy of social distancing with early detection and isolation, showing it is more efficient than social distancing alone.

Findings

Combined strategies reduce epidemic peak more effectively.

Shorter lockdowns are possible with early detection.

Simulation results specific to Italy support the approach.

Abstract

Social distancing, often in the form of lockdown, has been adopted by many countries as a way to contrast the spreading of COVID-19. We discuss the temporal aspects of social distancing in contrasting an epidemic diffusion. We argue that a strategy based uniquely on social distancing requires to maintain the relative measures for a very long time, while a more articulate strategy, which also uses early detection and prompt isolation, can be both more efficient on reducing the epidemic peak and allow to relax the social distancing measures after a much shorter time. We consider in more detail the situation in Italy, simulating the effect of different strategies through a recently introduced SIR-type epidemiological model. The short answer to the question in the title is: "it depends on what else you do".