President Biden has urged state leaders to implement statewide mask mandates to help curb the novel coronavirus' spread—but do mask mandates really work? CDC on Friday published two new Morbidity and Mortality Weekly Reports on the matter. Here's what they found.

Radio Advisory episode: Biden's plan for fighting Covid-19

Mask mandates linked to high rate of proper mask wearing at universities

For one of the new reports, CDC set out to determine whether mask mandates at universities were associated with a high rate of mask use in public places. CDC in the report noted that "[c]orrect use of face masks limits [novel coronavirus] transmission," and "[m]any institutions of higher education mandate masks in public indoor locations and outdoors when within six feet of others."

For the report, CDC researchers directly observed mask use at six universities with mask mandates and at nearby off-campus locations that also had mask mandates during September 2020 to November 2020. Overall, the researchers found that the universities had a high rate of mask use, at 85.5% of 17,200 people observed, as well as a high rate of proper mask use, at 89.7% of those observed and 76.7% of those wearing masks. CDC noted that proper mask use involves wearing a face covering over "the nose and mouth and secured under the chin."

Proper mask use was higher among people observed indoors, the researchers found, with 91.7% of people observed indoors wearing masks correctly. The researchers noted that the percentage of people observed indoors who were wearing masks correctly varied by the type of mask worn. Specifically, the researchers found that 96.8% of people wearing N95-type masks indoors wore them correctly; 92.2% of people wearing cloths masks indoors wore them correctly; and 78.9% of people wearing bandanas, scarves, and similar face coverings indoors wore them correctly.

The researchers found that mask use was substantially more common indoors, at 94%, than it was outdoors, at 67.6%. Mask use also was more common at indoor locations on campus, at 94.8%, than at nearby, indoor locations off campus, at 90.6%. According to the researchers, cloths masks were the most common type of mask used among people observed wearing them, at 68.3%. Surgical masks were the second-most common, at 25.7%, followed by gaiters at 3.8%, N95-type masks at 1.9%, and other face coverings—including bandanas and scarves—at 0.3%.

Ultimately, the researchers wrote that "[o]bserved indoor mask use was high at these six universities with mask mandates," and "[c]olleges and universities can use direct observation findings to tailor training and messaging toward increasing correct mask use."

Mask mandates associated with fewer Covid-19 hospitalizations

For the second report, CDC set out to determine whether statewide mask mandates were associated with fewer hospitalizations from Covid-19, the disease caused by the novel coronavirus. To do so, CDC researchers analyzed data from 10 sites that participated in the Covid-19 Associated Hospitalization Surveillance Network and were located in states that implemented statewide mask mandates during the period spanning from March 1, 2020, to Oct. 17, 2020.

The researchers found that after officials implemented statewide mask mandates, the 10 sites reported declines of up to 5.5 percentage points in their growth rates of weekly hospitalizations linked to Covid-19 among adults ages 18 to 64. The study compared these rates with the reported weekly growth in hospitalizations linked to Covid-19 among adults ages 18 to 64 during the four weeks leading up to the mask mandates' implementation, the researchers wrote.

Specifically, the researchers found that during the first two weeks after states implemented the mask mandates, there was a 2.1 percentage-point decline in reported weekly Covid-19 hospitalization growth rates among adults ages 18 to 39, as well as a 2.9 percentage-point drop among adults ages 40 to 64. At three weeks after implementation, reported weekly Covid-19 hospitalization growth rates dropped by 5.5 percentage points among people ages 18 to 39 and among those ages 40 to 64, the researchers wrote.

The researchers wrote that their findings have implications for America's response to the country's coronavirus epidemic. "Statewide mask mandates might be associated with reductions in [novel coronavirus] transmission and might contribute to reductions in Covid-19 hospitalization growth rates," they wrote, adding, "Mask-wearing is a component of a multipronged strategy to decrease exposure to and transmission of [the novel coronavirus] and reduce strain on the health care system, with likely direct effects on Covid-19 morbidity and associated mortality" (Mascarenhas/Langmaid, CNN, 2/5; Barrios et al., CDC Morbidity and Mortality Weekly Report, 2/5; Joo et al., CDC Morbidity and Mortality Weekly Report, 2/5; Wilson, The Hill, 2/5; Cirruzzo, U.S. News & World Report, 2/5).