June 8, 2020 - Shelter-in-place orders prevented millions of deaths and tens of millions of COVID-19 cases, according to two studies published in Nature on Monday.
The two studies used different methods but reached similar conclusions. One study, published by a team of U.S. researchers, calculated that lockdowns prevented more than 60 million infections in the U.S. The other study, published by the Imperial College London COVID-19 Response Team, calculated that shutdowns saved more than 3 million lives across Europe.
“Without these policies employed, we could have lived through a very different April and May,” Solomon Hsiang, lead researcher of the U.S. study and director of the University of California at Berkeley’s Global Policy Laboratory, told The Washington Post.
Hsiang and colleagues used an econometric model to estimate how more than 1,700 stay-at-home orders, business closures and travel bans changed the spread of the virus in six countries: China, France, Iran, Italy, South Korea and the U.S. They looked at how infection rates changed before and after local, regional and national restrictions.
Before shutdowns, infections were doubling every two days, the team concluded. After shutdowns, the growth rates slowed substantially. Over time that reduction compounded, which further slowed the spread of the virus.
In total, the six countries avoided about 62 million documented infections. The actual number could be about 530 million, the researchers said, because people with mild infections and people without symptoms often don’t get tested or diagnosed. In the U.S. alone, shutdown measures prevented 4.8 million diagnosed COVID-19 cases and perhaps 60 million “actual” infections.
The Imperial College London team used an epidemiological model to estimate transmission numbers for 11 European countries based on observed deaths. Overall, the countries prevented 3 million deaths and reduced the rate of infection by 81%. The shutdown orders achieved “epidemic control,” they wrote.
In a conference call with reporters on Monday, the research teams said economic activity should return with precautions such as physical distancing, face masks and hand hygiene.
“We’re not saying the country needs to stay locked down forever,” said Samir Bhatt, senior author of the Imperial College London paper.
While the virus may be receding in some areas, the researchers said, only about 4% of people in the countries studied have been infected so far.
“This is just the beginning of the epidemic,” Bhatt told the newspaper in an email. “We’re very far from herd immunity.”