The emergency paid sick leave benefit passed by Congress in March to deal with the coronavirus pandemic kept a significant number of Americans from getting COVID-19, according to a peer-reviewed study published Thursday in the journal Health Affairs .

Yet the benefit is set to expire at the end of the year, well before the pandemic is expected to let up.

The new sick leave provision prevented 400 coronavirus cases per day per state in the U.S., according to the paper from researchers at Cornell University and KOF Swiss Economic Institute in Zurich. That roughly translates to 15,000 cases per day prevented in the United States, or one prevented COVID-19 case for every 1,300 workers. The researchers did not look at mortality rates.

The emergency sick leave was part of the Families First Coronavirus Response Act , the second of three stimulus bills passed in the spring. It provided 10 days of paid sick leave to workers at small companies, with the government reimbursing the cost through a tax credit. (The law also provided some family leave for parents with children home from school.)

Republican lawmakers and business lobbyists carved out a major loophole in the law by not extending coverage to workers at companies with more than 500 employees. Still, about one-fifth of the workforce, or about 20 million workers, were newly eligible for sick leave thanks to the law, according to the research released this week.

The paper appears to be the first evaluation of the new benefit and comes from a widely respected team of researchers.

Like masks, paid sick leave is an important tool that can reduce COVID-19 transmission, Nicolas Ziebarth, an associate professor in the policy analysis and management department at Cornell University, told HuffPost on Friday

Its not a magic bullet, but its one tool thats been shown to work. Over and over again. Its one tool in the toolbox that helps to bring down case numbers, said Ziebarth, who worked on the study.

The fact that the U.S., unlike other developed countries, has no universal paid sick leave law might be part of the reason case rates here have been higher than in European countries during the pandemic, Ziebarth said.

A previous study from Ziebarth showed that flu rates in states with paid sick leave were 11% lower than in those without the benefit.

Unlike masks, which have become politicized in the United States and in his home country of Germany, paid sick leave has the added benefit of being fairly uncontroversial, he said. A majority of Americans do support the policy, surveys have shown.

A dozen states and Washington, D.C., do have provisions that let workers still get paid if they need to stay home sick. So, for the study, Ziebarth and his colleagues compared states that never had any paid sick leave law to those that already had something on the books. The idea was to see what happened to case rates after workers obtained a wholly new benefit. Its the kind of natural experiment that scientists covet.