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:

• 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
• U.S.: 4.8 million confirmed, 60 million total

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.

This article was provided by Bloomberg News.