Lockdowns and other public-health measures may have prevented about half a billion coronavirus infections in six countries, including China and the U.S.
The virus has now caused some 7 million reported cases of Covid-19, with more than 400,000 fatalities. Published Monday in the journal Nature, 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. 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:
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 U.S.
There 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.
A separate report in Nature said lockdowns, school closures and other non-pharmaceutical measures may have saved 3.1 million lives in Europe alone. The study from Imperial College London estimated reductions in transmission up until May 4 based on combined data from 11 European countries, including the U.K., Spain, Italy, Germany and Belgium.
"This data suggests that without any interventions, such as lockdown and school closures, there could have been many more deaths from Covid-19," said Samir Bhatt, one of the study's authors, in a statement. "Careful consideration should now be given to the continued measures that are needed to keep Sars-CoV-2 transmission under control."