As COVID-19 spreads around the world, more and more things such as conferences, schools, and large events such as SXSW are being canceled – an effort to halt the spread of the virus and reduce the strain on our healthcare system. Meanwhile, dangerous notions circulate: the idea that nearly everyone will get COVID-19 so distancing measures are irrelevant or the idea that we might as well just get it and be done with it.

In the last few days, different versions of a simple, yet powerful, graph show us why it’s worth trying to keep the number of cases low. The takeaway: protective measures, such as self-isolation and canceling large gatherings, will delay and decrease the outbreak peak, reduce the burden on hospitals at a given time, and decrease the overall number of cases.

But do social distancing measures actually work?

1. A very short thread on the power of data graphics and scientific communication. Roughly a week ago, some very smart person* sat down, drew this graph, and saved lives. (*It’s 2 AM. Without an economist subscription, I can’t quickly discover whom. Maybe someone can help.) pic.twitter.com/eU71Eu60eS — Carl T. Bergstrom (@CT_Bergstrom) March 6, 2020

Social distancing during the 1918 influenza pandemic

To answer this question, let’s take a look at the response of several cities during the 1918 influenza pandemic. A 2007 paper in PNAS documented the effects of the 1918 pandemic in various US cities based on when public health interventions began, what the interventions were, and how many interventions they enforced. Examples of public health interventions include isolation policies, closures of schools, churches, and other venues, bans of public gatherings, and more.

Cities that began interventions earlier had significantly lower peaks of pneumonia and influenza-related mortality. And cities that implemented four or more interventions had a lower median peak weekly death rate (65/100,000 people) versus 146/100,000 people from cities with three or fewer interventions.

The response between Philadelphia and St. Louis made a great case that social distancing does work. In Philadelphia, the first case was reported on Sept 17 and authorities downplayed the significance of the case. They even allowed a city-wide parade to happen on Sept. 28. School closures and bans on public gatherings did not happen until Oct.3, 16 days since the first case. Meanwhile, St. Louis had its first case on Oct 5 and the city implemented social distancing measures two days later.

What was the effect? The 14-day difference in response time between the two cities represents approximately 3-5 doubling times for the epidemic. The peak weekly death rate from pneumonia and influenza-related deaths was 257/100,000 people in Philadelphia. The same metric in St. Louis was 31/100,000.

From the graph, you can see that there was a second peak towards the end of the study period. This occurred only after the city relaxed on intervention measures. No cities in the study experienced a second wave while the interventions were still in place.

Lessons from 1918 influenza pandemic for today

The authors from the 1918 influenza study highlighted some lessons from the cities responses that could be applied to future pandemics:

The results stress that action from public health officials need to happen sooner rather than later

Communities that implement more interventions proactively have better outcomes that communities that introduce interventions reactively

In cases of severe pandemics, cities should maintain interventions longer than 2-8 weeks (the norm in 1918)

Don’t panic, be prepared, and think about collective changes in behaviors can have big impacts.

Coronavirus resources