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2 new studies show shutdowns were astonishingly effective

In the United States, the public health measures averted 60 million infections, researchers found.

Social distancing reminders are on display in preparation for the opening of nonessential shops on June 9, 2020, in Brighton, UK.
Closed businesses and social distancing helped avert millions of Covid-19 coronavirus infections and deaths.
Mike Hewitt/Getty Images
Umair Irfan is a correspondent at Vox writing about climate change, Covid-19, and energy policy. Irfan is also a regular contributor to the radio program Science Friday. Prior to Vox, he was a reporter for ClimateWire at E&E News.

Lockdowns, stay-at-home orders, closed schools, and canceled public events prevented millions of Covid-19 coronavirus cases and deaths, according to two new peer-reviewed studies in the journal Nature.

One of the studies estimated the number of Covid-19 cases with and without these tough interventions. They found that in six countries, including China and the US, pandemic control policies had a huge effect. In the United States alone, the measures stopped 4.8 million more confirmed cases of Covid-19 and up to 60 million infections in total. In China, they prevented 285 million infections.

In the second study, researchers looked at the number of deaths from Covid-19 in 11 countries in Europe. They found that 3.1 million deaths in these countries were avoided with pandemic control measures.

It’s good news, and yet the pandemic continues to rage. There have now been more than 7 million confirmed cases of the disease worldwide, with many more lurking undetected.

Some countries, cities, and state governments in the US have begun to relax restrictions, even before meeting the criteria for reopening. And the course of the pandemic in the US has grown more uncertain with tens of thousands of protesters gathering to rally against police violence.

But these studies show yet again that no matter how painful they are, shutdowns do work at saving lives and reducing the burden on the health care system. The questions now are how much more of these restrictions will the world continue to tolerate, whether they’ll have to resume once lifted to counter new waves of the disease, and what strategies may emerge to replace them.

Closing economies and shutting down public life prevented millions of infections and deaths

In one of the studies, led by Solomon Hsiang, director of the Global Policy Laboratory at the University of California Berkeley, researchers looked at policies in China, France, Iran, Italy, South Korea, and the US to control the virus. The researchers examined 1,717 “non-pharmaceutical interventions” across these countries with real-world data and used econometric methods to trace the effects induced by these changes. Interventions included things like closing schools, declaring a state of emergency, banning travel, home isolation, and paid sick leave.

They found that in the early stages of the pandemic, cases grew by about 38 percent per day without any interventions. But measures to control the pandemic like canceling large gatherings “significantly and substantially slowed this growth.”

Taken together, such tactics prevented 62 million confirmed Covid-19 cases around the world. And since tests only find a small fraction of the total cases of the disease, researchers say that this estimate corresponds to about 530 million total infections around the world that were avoided.

The scale of the effect, however, changed depending on the country, as you can see in this table:

Shutdowns prevented millions of Covid-19 infections

Country Confirmed Covid-19 Cases Averted Total Covid-19 Cases Averted
Country Confirmed Covid-19 Cases Averted Total Covid-19 Cases Averted
China 37 million 285 million
South Korea 11.5 million 38 million
Iran 5 million 54 million
US 4.8 million 60 million
Italy 2.1 million 49 million
France 1.4 million 45 million
Hsiang et al./Nature

However, it’s difficult to tease out what specific policies proved most effective, and under what circumstances. It appears that home isolation, lockdowns, and business closures were among the more effective tactics, but the authors noted that there is uncertainty around the scale of their impacts. You can see how some of these tactics fared in the chart below (the watermark indicates the chart is from an accelerated preview version of the paper):

Chart showing how policies affected the growth rate of Covid-19 in different countries.
The effects of individual policies in slowing the spread of Covid-19 are hard to track and vary a lot between countries.
Hsiang et al./Nature

And it’s clear that there can be a lot of variation even within a country, as you can see in this animation comparing confirmed cases in the United States to expected cases without policies over time:

Animation of Coivd-19 cases rising in the United States
This animation compares the growth in confirmed Covid-19 cases in the US as observed (left) and as expected without any control policies (right).
Hsiang Global Policy Lab, UC Berkeley

Part of the variation is due to the timing of when these measures took effect. Researchers wrote that “seemingly small delays in policy deployment likely produced dramatically different health outcomes.” The earlier shutdown measures were implemented, the more Covid-19 cases were avoided. South Korea and the US, for instance, reported their first confirmed cases of the virus on the same day, January 21. But South Korea quickly started closing down public places and ramping up testing, while the United States lagged far behind.

And because the disease spreads at an exponential rate in its early stages, a difference of a few days has a large ripple effect.

It echoes an earlier finding that the US could have avoided 36,000 deaths from Covid-19 if the country implemented pandemic control measures just one week earlier. Those findings, however, were reported in a pre-print study, meaning they hadn’t undergone peer review.

The second Nature study, led by Seth Flaxman, Swapnil Mishra, Axel Gandy, and Samir Bhatt at Imperial College London, took a different modeling approach to examine whether shutdowns saved lives. They examined 11 countries in Europe — Austria, Belgium, Denmark, France, Germany, Italy, Norway, Spain, Sweden, Switzerland, the United Kingdom — and calculated how far the disease had spread, extrapolating backward from the number of observed deaths from the virus. The logic here is that deaths from the virus are the most incontrovertible data available about the impact of the disease.

By May 4, between 12 million and 15 million people had been infected by the coronavirus in these countries, researchers found. The researchers went on to estimate how tactics like closing shops, schools, and public spaces affected the spread of the virus, simulating what would have happened if illness continued to spread unchecked.

In the 11 countries studied, the interventions drove the transmission rate of the virus down within the population such that each infected person subsequently infected less than one other person on average.

“This reduction likely prevented the exponential growth of infections that would have resulted in the horrible scenes we saw in Lombardy [Italy] in March,” said co-author Bhatt during a call with reporters. Such measures averted 3.1 million deaths in these countries up to May 5.

Graph comparing deaths in Europe with and without shutdowns to control Covid-19.
The total number of deaths with interventions (orange) in 11 countries is lower than it would have been without any measures to control Covid-19 (green).
Flaxman et al./Nature

“When looking at simplistic counterfactuals over the whole epidemic the number of potential deaths averted is substantial,” researchers wrote. “We cannot say for certain that the current measures will continue to control the epidemic in Europe; however, if current trends continue, there is reason for optimism.”

Both of these papers align with another study published last month in Health Affairs that reported the spread of Covid-19 would have been 35 times greater in the United States without policies like shelter-in-place orders.

Together, these findings show that public health measures to limit the spread of the pandemic worked.

Shutdowns worked. Now what?

Beyond limiting the number of people infected and killed by the virus, the point of these social interventions was to buy time. With drastic restrictions on movement and activities to slow the spread of the virus, health officials could build up capacity for testing, contact tracing, and treatment. Eventually, a viable treatment or vaccine would emerge and gradually immunity would rise in the population until the virus can no longer spread easily.

The problem is that these measures can’t continue indefinitely. The social and economic costs have been immense, which in turn have their own health costs. And some countries and many US states have begun to lift their restrictions.

Yet it may still be too soon for many parts of the world to relax, as herd immunity remains far off and new cases of Covid-19 continue to mount. Arizona lifted its stay-at-home order in May, but infections are on the rise. Several countries are also seeing an alarming rise in cases even as they relax.

“The virus is very much with us, and arguably we are only at the end of the beginning,” Bhatt said. “Care must be exercised until such time as a vaccine or treatment becomes available.”

A different, more measured strategy will be needed to contain the pandemic in the days ahead, as Vox’s Dylan Scott explained:

We have to seek a middle ground between maintaining the social distancing policies that have worked to slow the spread and the natural need for social interaction and the urgency of relieving the economic crisis.

But all of these discussions are undergirded by one important reality. Many people, the vast majority of us, are still susceptible to Covid-19. A sloppy end to social distancing could mean a rapid rebound in the virus’s spread.

It will likely be much harder to reimpose pandemic interventions if cases spike again, but it’s not clear what strategy will ultimately prove successful. With so many different parts of the world pursuing their own paths, scientists will have a massive natural experiment to gauge what works, but some of these lessons will be learned the hard way.

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