CDC on Wednesday updated its recommendations on how Americans should wear face masks to protect themselves against the novel coronavirus, calling on people to now wear two masks or one tightly fitting mask.

Do mask mandates work? Here's what new CDC research reveals.

CDC finds tightly fitting masks, double masking can significantly reduce coronavirus exposure

CDC issued the new recommendations based on findings from a new Morbidity and Mortality Weekly Report, in which CDC researchers found that people can reduce their exposure to the novel coronavirus by using certain methods to improve the fit of their masks.

One of those methods involves wearing a cloth mask over a surgical mask, which is known as double masking. CDC researchers found that, when both a "source and receiver" were double masked, the cumulative exposure of the receiver to potentially infectious aerosols dropped by 96.4%.

Another method involves wearing a tightly fitting surgical mask by knotting the ear loops of the mask and then tucking in and flattening extra material, which is known as knotting and tucking masks. According to the researchers, experiments showed that the cumulative exposure of the receiver to potentially infectious aerosols dropped by 95.9% when both a source and receiver wore knotted and tucked surgical masks.

CDC researchers also found that people can reduce their potential exposure to the novel coronavirus by properly fitting their masks using so-called "mask fitters," which are a frames designed to contour the face, or by "placing a sleeve made of sheer nylon hosiery material around the neck and pulling it up over either a cloth or medical procedure mask," according to the report.

Overall, the researchers concluded that "universal masking is a highly effective means to slow the spread of [novel coronavirus] when combined with other protective measures, such as physical distancing, avoiding crowds and poorly ventilated indoor spaces, and good hand hygiene," and that a "good fit can increase overall mask efficiency."

CDC officials urge Americans to wear 'well-fitting' masks

CDC officials are calling on Americans to begin double masking or ensuring their masks have a tight fit, especially because new, more-contagious variants of the novel coronavirus have started spreading throughout the United States.

John Brooks, a medical epidemiologist at CDC and the report's lead author, said, "We know that universal masking works. And now these [new coronavirus] variants are circulating … whatever we can do to improve the fit of a mask to make it work better, the faster we can end this pandemic."

Brooks noted that CDC's report was based on laboratory experiments that used three-ply surgical and cloth masks, and it's unclear how its recommendations will perform broadly in the real world. "But it's very clear evidence that the more of us who wear masks and the better the mask fits, the more each of us benefit individually," Brooks said.

During a White House press briefing on Wednesday, CDC Director Rochelle Walensky also urged Americans to wear "a well-fitting mask" that has two or more layers. "With [coronavirus] cases, hospitalizations, and deaths still very high, now is not the time to roll back mask requirements," Walensky said. "The bottom line is this: Masks work, and they work when they have a good fit and are worn correctly."

Where America's coronavirus epidemic stands

The new recommendations come as data from the past two weeks indicates America's coronavirus epidemic is improving when compared with the peak in new coronavirus cases, hospitalizations, and deaths the country experienced last month. However, the reported rates of each of those metrics remain high, and experts say the epidemic's recent progress is on shaky ground because of the newly emerging coronavirus variants and some states' moves to scale back restrictions intended to mitigate the virus's spread.

According to data compiled by the New York Times, U.S. officials on Wednesday reported about 94,893 new cases of the novel coronavirus, marking the fourth consecutive day that U.S. officials reported fewer than 100,000 new cases of the virus. As of Thursday morning, officials had reported a total of about 27.3 million cases of the virus since America's epidemic began.

According to the Times, the United States' average daily number of newly reported coronavirus cases over the past week was 104,559—which is down by 36% when compared with the average from two weeks ago, when the United States was in the midst of its worst peak in newly reported cases.

As of Thursday morning, data from the Times showed that the rates of newly reported coronavirus cases were "staying high" in Alaska, South Dakota, and Vermont, which have each reported a daily average of at least 15 newly reported cases per 100,000 people over the past week. In contrast, rates of newly reported coronavirus cases were "staying low" as of Thursday morning in Guam, Hawaii, Michigan, North Dakota, Oregon, Puerto Rico, U.S. Virgin Islands, Washington, and Wyoming.

All other states and Washington, D.C., had been seeing comparatively higher rates of coronavirus transmission, but the daily average of newly reported coronavirus cases over the past seven days in those areas was "going down" as of Thursday morning, according to the Times' data.

U.S. hospitalizations for Covid-19, the disease caused by the novel coronavirus, remained high as of Wednesday, but were down by about 8% last week when compared with the previous week, Axios' "Vitals" reports. According to data from The Atlantic's COVID Tracking Project, there were 76,979 Americans with Covid-19 hospitalized for treatment on Wednesday, including 15,788 who were receiving care in an ICU and 5,121 who were on a ventilator. Wednesday marked the seventh consecutive day that fewer than 90,000 Americans with Covid-19 were hospitalized for treatment.

Similarly, the United States' rate of newly reported deaths linked to the novel coronavirus has declined over the past two weeks, though it also remains high. According to "Vitals," the number of newly reported deaths linked to the coronavirus in the country dropped by 3% last week when compared with the previous week.

According to data from the Times, U.S. officials reported about 3,255 new deaths linked to the virus on Wednesday. As of Thursday morning, officials had reported a total of about 471,346 U.S. deaths linked to the virus since the country's epidemic began.

(Fernandez, Axios, 2/10; Rabin/Stolberg, New York Times, 2/10; Sun/Nirappil, Washington Post, 2/10; Cohen, Roll Call, 2/10; Stobbe, Associated Press, 2/10; CDC Morbidity and Mortality Weekly Report, 2/10; New York Times, 2/11; Owens, "Vitals," Axios, 2/11; "COVID Tracking Project," The Atlantic, accessed 2/11).