COVID-19: What is ‘flattening the curve,’ and will it work?

Updated: Apr 3, 2020

“Flatten the curve” is perfect shorthand to describe the effort being undertaken right now around the world to control the spread of COVID-19. The idea is that, by social distancing, closing schools and museums and sacrificing the mass gatherings that create a sense of community, countries can slow the increase in the number of cases and, hopefully, protect their medical systems from being overwhelmed.

The “curve” refers to something called an epi curve, a graph line that charts the rise, peak and fall of existing infections over time.

“Collectively, First Nations are high risk for tragic outcomes and our vulnerable are extremely high risk. Please stay home and practice social distancing to flatten the curve.” Ontario Regional Chief, RoseAnne Archibald

Flatten the curve

Health authorities around the world have been unable to completely prevent COVID-19’s spread. If cases double every six days, then hospitals, and intensive care units (ICUs) in particular, will be quickly overwhelmed, leaving patients without the necessary care.

But the growth rate can be slowed by reducing the average number of cases that a single case gives rise to.

In doing so, the same number of people will probably be infected, and the epidemic will last longer, but the number of severe cases will be spread out. This means that if you plot a graph of the number of cases over time, the rising and falling curve is longer but its peak is lower. By “flattening the curve” in this way, ICUs will be less likely to run out of capacity.

Flattening the curve is another way of saying slowing the spread. The epidemic is lengthened, but we reduce the number of severe cases, causing less burden on public health systems.

As there is currently no vaccine or specific drug for COVID-19, the only ways we can reduce transmission is through good hygiene, isolating suspected cases, and by social distancing measures such as cancelling large events and closing schools.

How much social distancing is required to flatten the curve enough to stop hospitals being overwhelmed? Is it enough to quarantine people who have been in contact with confirmed cases? Do we need widespread closure of events, schools and workplaces?

Answers to these questions require mathematical modelling.

As we are still in the early stages of the COVID-19 outbreak and there is great uncertainty about the characteristics of this virus. To accurately forecast COVID-19’s growth, the underlying dynamics of transmission need to be determined.

These are driven by factors including:

  1. How many people on average does an individual infect? (the “reproduction number” which, according to the World Health Organisation, is currently between 1.4–2.5 people)

  2. How long until the onset of symptoms? (the “incubation period”, which is estimated to be 5.1 days)

  3. What proportion of transmission occurs prior to the onset of symptoms, if any?

As such data is collected and integrated into models over the coming months, we will be better placed to offer accurate predictions about the course of COVID-19.

Until then, it’s better to err on the side of caution and take swift action to slow transmission, rather than risk a spike in cases, and put strain on our health system.

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