More widespread wearing of face masks could prevent tens of thousands of deaths by COVID-19, epidemiologists and mathematicians project.

A model from the University of Washington's Institute for Health Metrics and Evaluation shows that near-universal wearing of cloth or homemade masks could prevent between 17,742 and 28,030 deaths across the US before Oct. 1.

The group, which advises the White House as well as state and local governments, is submitting the model for peer review, says Theo Vos, Professor of Health Metrics Sciences at IHME.

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Another projection developed by researchers at Arizona State University in April showed that 24–65% of projected deaths could be prevented in Washington state in April and May if 80% of people wore cloth or homemade masks in public.

These projections shed light on the promises face masks might hold as COVID-19 cases surge in some states and more local authorities mandate the wearing of face masks.

Texas is now mandating face masks in public in most of the state; Jacksonville Fl, host city of the Republican National Convention in August, mandated wearing face masks in public and indoor locations where people cannot otherwise social distance on June 29.

Republican leaders including Vice President Mike Pence, Majority Leader Mitch McConnell, Tim Scott of South Carolina, Lamar Alexander of Tennessee and Marco Rubio of Florida, have joined public health officials urging the public to wear facemasks. Dr. Anthony Fauci and members of Congress appealed to the public to wear face masks in a congressional hearing Tuesday. And President Trump, in a change of tone, told Fox Business on Wednesday he's 'all for masks.'

But public health professionals lament that trust in face masks is hampered by the government's earlier recommendation against them.

Fauci told TheStreet mid-June that he did not recommend face masks at the beginning of the outbreak to conserve supplies for healthcare workers. On Thursday Fauci told NPR that the administration's initial ambivalence towards face masks was 'detrimental in getting the message across.'

The World Health Organization gave NPR the same reasoning for not recommending masks to the general public in April. The organization has since updated its guidelines.

Benjamin Cowling, Professor and head of the Division of Epidemiology and Biostatistics in the School of Public Health at the University of Hong Kong, has studied effects of face masks for ten years and co-wrote a commentary in The Lancet advocating more face mask usage in March. He says while he understands the authorities' desire to preserve supplies for medical workers, the messaging made the public distrust masks.

"Few months ago, medical experts were saying that they don't work and you don't need them. And now suddenly, without any change in the evidence base, they're suddenly saying that they do work and you should wear them." Cowling says, 'I think that that's unhelpful.

Mask adoption in the US has been uneven. A survey from the data collection firm Premise shows that the percentage of people who 'always wear a mask when going out' ranges from 15% in Tennessee to 62% in Massachusetts as of June 19.

For both ASU and IHME's models, the proportion of deaths face masks could prevent differs from location to location and during different stages of the pandemic because transmission rates in the community at the time of projection affect outcomes.

In ASU's model, widespread community transmission would call for more effective face masks - for example, the surgical masks used in hospitals - to significantly reduce the number of projected deaths. But in places where transmission is not as widespread, most people wearing simple cloth masks would be able to prevent a significant portion of deaths.

In IHME's model, the more people each infected individual can spread the virus to, the more deaths masking can prevent. It also projects that the virus would follow seasonal patterns and pick up again in the fall. Vos says this means places that have relatively safe levels of the spread now could see more pressure to contain the virus later.

"The use of masks...in those places is going to become a lot more marked and beneficial." Vos says.

Regardless of community transmission rates, both models show that the more universal face masks are worn, the more deaths can be prevented.

It's difficult to know whether the projections are correct because it's difficult to know how the public is actually wearing masks. But considering that research on face masks show that they can tamp down transmission, modellers agree that they should help save lives when worn by a large portion of the population.

"Clearly, clearly the data shows that every model and study that we have seen, every public health policy in the world has said exactly the same thing," says Abba Gumel, who led the ASU project, 'We have to wear a face mask.'

Andrea Hsu and Courtney Dorning produced and edited the audio version of this story. contributed to this story

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