Public health measures can slow the spread of coronavirus to keep the number infected at any one time at a manageable level

In their response to the coronavirus outbreak, public health experts and government officials have repeatedly referenced the importance of “flattening the curve”. But what does this mean, exactly?

When faced by a threat such as Covid-19, epidemiologists often look for two important numbers: how infectious a disease is, quantified by the number of people infected by each person infected, and the total number of people who die as a result of catching the illness.

Covid-19 appears to be more infectious than the common flu and the cause of a higher rate of deaths. But these rates aren’t immutable, with the differing pattern of the virus’s spread in various countries showing that interventions can make a big difference.

Without protective measures to slow the spread of Covid-19, there is likely to be a large spike in infections in a short period of time.

This scenario risks overwhelming health systems, with the parlous situation in Italy illustrating the dangers of when a country is hit by a wave of new cases. Hospitals can struggle to cope with the influx, leading to a higher mortality rate.

A key goal of public health officials now is to avoid a huge peak in Covid-19 cases in favour of a slower growth that becomes a moderate plateau. Infections still occur, but over a longer period – and “flattening the curve” turns the steep mountain of cases into a more sedate hillock.

This more gentle increase in cases gives health systems the time to adapt and absorb the new patients, ensure that the virus is not spread further and effectively treat the most vulnerable. Many of the measures we have seen around the world to restrict travel and large gatherings are aimed at ensuring coronavirus does not run riot.

“Through aggressive sanitation efforts, diligent hand-washing, canceling large gatherings, minimizing travel, teleworking, and similar measures we can *flatten out the epidemic curve*, keeping the number of people simultaneously infected at a low enough level to be manageable,” tweeted Carl Bergstrom, a biologist at the University of Washington who co-created a widely shared graph illustrating the flattening of the curve.

“The steps we take now, individually and as a community, will determine the trajectory of the #COVID19 epidemic. This in turn will determine how many lives are lost. It is not just a matter of protecting yourself; it is a matter of protecting the most vulnerable among us.”