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UNITED STATES (CNN) – The decision to wear a mask or not has divided Americans, but a new study suggests face coverings have significantly reduced the number of new coronavirus cases.

Wearing face masks in public has prevented up to 450,000 new cases, according to the research.

The study, published online in the Health Affairs journal, estimates between 230,000 to 450,000 cases of the coronavirus were prevented in the states that enacted requirements for mask use between April 8 and May 15.

Researchers say wearing face masks in public reduced the daily number of coronavirus cases by as much as 2% in Washington D.C. and the 15 states that mandated their use, compared to the states that did not.

The longer the mandates were in place, the higher the reduction in cases.

Researchers also looked at 20 states that imposed employee-only mandates, but not public mask use and did not find a significant impact on the spread of the coronavirus in those states.

The study did have some limitations, including the inability to measure the actual use of face coverings in any community. Researchers were also only able to measure confirmed cases, despite evidence that infection rates in some communities were higher.