RALEIGH, N.C. (WNCN) — States that required people to wear face coverings in public saw significant drops in the daily growth rate of COVID-19, according to a study.

The authors of the study — published this week by healthaffairs.org — claim it “provides direct evidence on the effectiveness of widespread community use of face masks.”

Its publication is particularly timely with the city of Raleigh’s requirement of the use of face coverings in public places taking effect Friday. That comes as the state set a single-day high for COVID-19-related hospitalizations for the third consecutive day and the eighth time in 11 days, with 857 people in the hospital Thursday.

The authors, researchers from the University of Iowa, looked at the 15 states, plus the District of Columbia, with statewide executive orders or gubernatorial directives that mandated the use of masks from April 8-May 15.

They found that the COVID-19 daily growth rates at the county level dropped almost immediately — decreasing by 0.9 percentage points within the first five days after going into effect. The rate continued to fall, dipping 2 percentage points more than three weeks after enactment.

“There is a significant decline in daily COVID-19 growth rate after mandating facial covers in public, with the effect increasing over time after signing the order,” according to the study.

They say the five-day declines in growth rate are “broadly consistent” with the timing of other social distancing measures, including the closing of certain businesses.

They also estimate that more than 200,000 cases — and as many as 450,000 — by May 22 may have been avoided because of those mandates, adding that those estimates should be viewed “cautiously.”

And another study by British researchers at Cambridge and Greenwich universities looked at the effect of face coverings on the effective reproductive number of the virus. 

Also known as the Rt or the Re, the figure is the average number of people a sick person will go on to infect. A number greater than 1 indicates exponential growth while a number less than 1 is a sign the spread of a virus can be controlled.

The British study found that the act of all people properly wearing face coverings in public is twice as effective at reducing the Rt than if they are only worn by people showing symptoms. And if more than half the population wears masks, the study concludes, the Rt would drop below 1 — making it easier to manage the pandemic.

Despite the ongoing public debate about the use of masks, Dr. Cameron Wolfe, an infectious disease specialist from Duke University, said Thursday that the scientific community is more united on their effectiveness.

“The consensus seemed really strong to me that the wearing of any mask, including cloth masks that folks will now see for sale widely, is very satisfactory at me preventing you getting sick,” Wolfe said.