Lockdowns and other public-health measures may have prevented about half a billion coronavirus infections in six countries, including China and the U.S.


“We find that the deployment of anti-contagion policies in all six countries significantly and substantially slowed the pandemic,” the researchers write in their paper. Solomon Hsiang is the lead author on the Nature article titled, “The effect of large-scale anti-contagion policies on the COVID-19 pandemic.”


The virus has now caused some 7 million reported cases of Covid-19, with more than 400,000 fatalities. The first peer-reviewed analysis of the impact of health policies suggests that the toll would have been vastly worse without lockdowns, social distancing, travel restrictions and other interventions.


They found that “seemingly small delays in policy deployment likely produced dramatically different health outcomes.”


Their central estimates suggest that there would be roughly 37 million more cumulative confirmed cases (corresponding to 285 million more total infections, including the confirmed cases) in China had preventive measures not been taken.


The U.S. would have had 4.8 million more confirmed cases (60 million total infections) had it never enacted any anti-contagion policies.


The policy deployments the measured included travel restrictions, social distancing through cancellations of events and suspensions of educational/commercial/religious activities, quarantines and lockdowns, and additional policies such as emergency declarations and expansions of paid sick leave, from the earliest available dates to April 6, 2020.


Home isolation, business closures and lockdowns produced the clearest benefits, the study found. Travel restrictions and bans on gatherings had good results in Italy and Iran, but their impact was less clear in the was no strong evidence that school closures had an effect in any country, and the team said that more research should be done to inform decisions on opening or closing schools.


Most interventions took three weeks to achieve their full impact. Now that some countries are relaxing policies, “we might reasonably expect signals of any renewed spread to emerge on a similar two- to three-week time frame,” Hsiang said. –


They estimate that across these six countries, interventions prevented or delayed as many as 62 million confirmed coronavirus cases, which in turn helped avert roughly 530 million total infections.

Many coronavirus infections are relatively mild, and most of the roughly 500 million averted cases would have gone undetected, according to the study.“Seemingly small delays in policy deployment likely produced dramatically different health outcomes” in different countries, said Solomon Hsiang, lead author on the paper from the University of California, Berkeley. The authors distinguished between prevention of cases that would have been reported and those that would never have been diagnosed.


Here’s a breakdown of estimated cases prevented by country:

China: 37 million confirmed cases, 285 million total cases
South Korea: 11.5 million confirmed, 38 million total
Italy: 2.1 million confirmed, 49 million total
Iran: 5 million confirmed, 54 million total
France: 1.4 million confirmed, 45 million total
US: 4.8 million confirmed, 60 million total


The researchers measured how much more than 1,700 local, regional and national public health policies these policies slowed the growth rate of infections. To do this, they compared the growth rate of infections within hundreds of sub-national regions before and after each of these policies was implemented locally.


They estimate that if large-scale anti-contagion policies had not been deployed, there would be roughly 465 × the observed number of confirmed cases in China; 17 × in Italy; and 14 × in the U.S.


The results reflect when anti-contagion policies were implemented well as how many localities deployed them and for how long.