New evidence shows that cloth face coverings slow coronavirus spread

With coronavirus spreading faster than ever in the U.S., two new studies are providing more evidence that universal face masking is an effective tool to help slow the spread of the virus. The new research comes just as Walmart, the nation’s biggest retailer, said it will require all customers to wear a mask.

This week, the director of the Centers for Disease Control and Prevention said that if everyone in America wore a mask, washed hands frequently and practiced social distancing, the spread of the virus would be under control in one to two months.

“Cloth face coverings are one of the most powerful weapons we have to slow and stop the spread of the virus — particularly when used universally within a community setting,” Dr. Robert Redfield said in a statement. “All Americans have a responsibility to protect themselves, their families and their communities.”

Saskia Popescu, an infectious disease epidemiologist at the University of Arizona, said the plea from the CDC shows the U.S. needs to unite to make a collective effort on masking.

“Now is the time for us to work together, and universal masking is one such effort that can make a huge impact,” Popescu wrote in an email.

Two new, real-world studies showed how effective face coverings are in slowing coronavirus spread.

In the first, researchers at Massachusetts General Hospital in Boston monitored how wearing a mask affected transmission rates of SARS-CoV-2, the virus that causes COVID-19, among hospital health care workers.

Researchers tracked the infection rates among staff before and after the mask mandate.

Before masking, the positivity rate of testing was increasing exponentially at a rate of 1.16 percent per day. After masks were required, the positivity rate among health care workers started to slowly decline at rate of 0.49 percent per day.

“It's almost a stress test of masking, and it showed that masking is effective in terms of reducing infection from COVID.” said Dr. Deepak Bhatt, lead author of the study and a professor at Harvard Medical School and the executive director of interventional cardiovascular programs at Brigham and Women’s Hospital.

Related: No measure by itself completely prevents the virus, but now there's evidence that face masks, social distancing and eye protection greatly reduce risk.

Bhatt hopes the research will help ease political resistance to wearing a mask.

“What we're doing here is bringing out some science," Bhatt said. "This isn't politics. This isn't blaming anyone. This isn't us trying to second guess what's already happened, but rather allow a way hopefully for us all to move forward together and support masking."

A separate report released by the CDC Wednesday found that masks protected against the virus spread in a Springfield, Missouri, hair salon.

Two hair stylists at the salon developed respiratory symptoms but had continued working until they received positive test results for coronavirus.

Between the two stylists, 139 clients had been potentially exposed between the time the stylists developed symptoms to when they received the test results. Both of the stylists and their clients wore face coverings while they were in the salon.

Through contact tracing efforts, local officials found no symptomatic cases reported from exposure to the hair stylists. In addition, 67 of the clients who were exposed were tested and all of them were negative.

“This is a beautiful experiment; you couldn't have designed a better one to show that masks work," Dr. Carlos del Rio, an infectious disease specialist and chair of the department of global health at Emory University, told NBC News.

Related: COVID-19 testing has changed since the coronavirus outbreak began. Here's what you need to know before getting a test — and what to expect when you're there.

According to Del Rio, one limitation of the study was that not all clients underwent testing, leaving a possibility of asymptomatic infections. Recent CDC estimates say that as many as 40 percent of infections may be asymptomatic.

“Ideally you would have liked to test everybody," Del Rio said. "But the reality is, it shows pretty nicely that masks work.”

Hair salons remain open in Texas, Arizona, and Florida where cases are surging and ICU bed capacity is dwindling.

Popescu, who resides in Arizona and is seeing the devastating effects of the epidemic in her state, has observed an increase in mask use and attributes this to the recent media attention and mask mandates in many states and communities.

“Now is the time for us to rally around public health efforts, help reduce the strain on health care workers and hospitals, and keep ourselves and our loved ones safe,” she said.