COVID-19 cases higher in schools without mask policies, CDC studies show

Why CDC recommends masks indoors, even for fully vaccinated people

The CDC updated its mask guidance on July 20, saying that people who live in areas with high COVID-19 transmission, should wear masks indoors regardless of vaccination status.

WASHINGTON - On Friday, the U.S. Centers for Disease Control and Prevention released three studies highlighting the importance of using layered prevention strategies including universal masking to stop the spread of the novel coronavirus in schools.

The studies, published in the site’s "Morbidity and Mortality Weekly Report," found that school districts without a universal masking policy in place were more likely to have COVID-19 outbreaks. Nationwide, counties without masking requirements saw the number of pediatric COVID-19 cases increase nearly twice as quickly during this same period.

One of the studies revealed that Arizona schools in two of the state’s most populous counties were 3.5 times more likely to have COVID-19 outbreaks if they did not have a mask requirement at the start of school compared with schools that required universal masking on day one.

Meanwhile, another study found that during the two weeks following the start of school, the average change in pediatric COVID-19 case rates was lower among counties with school mask requirements (16.32 per 100,000/day) compared with counties without school mask requirements (34.85 cases per 100,000/day).

The CDC highlighted a third report which studied COVID-19-related school closures and found that despite an estimated 1,801 school closures so far this school year, 96% of public schools have been able to remain open for full in-person learning.

"These studies continue to demonstrate the importance and effectiveness of CDC’s Guidance for COVID-19 Prevention in K-12 Schools to help districts ensure safer in-person learning and stop the spread of COVID-19," the CDC wrote in a press release. "Promoting vaccination of eligible persons, mask wearing, and screening testing are all proven methods to continue to work towards the end of the COVID-19 pandemic."

In late July, The American Academy of Pediatrics recommended universal masking in schools, even for those who are vaccinated against the virus that causes COVID-19.

Dr. Anthony Fauci said the guidance was out of an abundance of caution due to the rise in cases blamed on the delta variant of the coronavirus.

The academy said getting children back into schools and learning alongside their fellow students and teachers was the top priority and that "we all play a role in making sure it happens safely."

"The pandemic has taken a heartbreaking toll on children, and it’s not just their education that has suffered but their mental, emotional and physical health. Combining layers of protection that include vaccinations, masking and clean hands hygiene will make in-person learning safe and possible for everyone," said Sonja O’Leary, MD, FAAP, chair of the AAP Council on School Health.

Just a few days later after the academy called for kids to be masked up, the CDC changed its mask guidelines on July 27 for people who have been fully vaccinated against COVID-19, citing new information about the ability of the delta variant to spread by those who have been vaccinated.

The CDC added that everyone in K-12 schools should wear masks, regardless of vaccination status.

CDC Director Dr. Rochelle Walensky said the high transmissibility of the delta variant was behind the agency’s change in guidelines.

Masks have been a point of contention as U.S. schools reopen amid rising numbers of coronavirus cases. Questions about whether to require them have caused turmoil among parents and politicians, with some Republican governors banning mask mandates even as President Joe Biden threatens legal action against them.

But a recent poll from the Associated Press-NORC Center for Public Affairs Research found that a majority of Americans say they support mask mandates for students and teachers in K-12 schools

About 6 in 10 Americans say students and teachers should be required to wear face masks while in school, according to the poll. Similar shares say teachers and eligible students should also be required to receive a COVID-19 vaccine.

In a reflection of that polarizing debate, the poll finds a wide partisan divide. About 3 in 10 Republicans said they favor mask requirements for students and teachers, compared with about 8 in 10 Democrats. There was a similar split over vaccine mandates in schools.

In some areas with school mask mandates, tensions have flared in recent weeks. Protesters opposing mask requirements have filled school board meetings from Maryland to California, in some cases disrupting meetings and forcing them to postpone.

Most states allow school districts to set their own mask policies, but some including California, Illinois and Louisiana are requiring masks for students and teachers statewide. At least eight Republican-led states have moved to ban universal mask mandates in schools, including in Texas, Florida and Tennessee.

Medical experts have said masks are a vital part of the best line of defense against the spread of COVID-19, but facial coverings don’t act as a substitute for other precautionary measures like social distancing, personal hygiene and getting vaccinated.

Masks can help the wearer get less sick with COVID-19, even if they do become infected from an unmasked person.

In November, the CDC referred to a study led by Japanese researchers that found masks block about 60% of the amount of virus that comes out of an infected person. When an uninfected person wearing a mask is near an infected person who isn’t wearing one, the amount of virus the uninfected person inhaled fell by up to 50%.

But when both people were wearing masks, the best result was observed. The decline in virus particles reaching the second person was close to 70%.

Dr. Richard Davis, who is the clinical microbiology lab director at Providence Sacred Heart Medical Center in Spokane, Washington, tweeted a series of photos last year that showcased two demonstrations aimed at understanding how effective face masks are at blocking respiratory droplets from an individual’s mouth, while also illustrating the importance of social distancing.

Using a standard triple-layer hospital issue surgical mask, Davis sneezed, sang, talked and coughed toward an agar culture plate with and without a mask.

Agar culture plates are Petri dishes filled with agar, a gelatinous substance obtained from red algea to culture, or help multiply, microorganisms. After performing each action, Davis said bacteria colonies formed in the dishes where the respiratory droplets emitted from his mouth landed.

"Bacteria colonies show where droplets landed. A mask blocks virtually all of them," Davis wrote in a caption for the post.

In another demonstration, Davis showed how keeping one’s distance makes a difference in stopping the spread of respiratory droplets.

FILE - Photograph of Dr. Rich Davis demonstrating how social distancing with a face mask impacts the spread of respiratory droplets.

Pictures show that standing two feet apart with no mask practically covered the Petri dish with bacteria. Davis’ respiratory droplets also managed to land on the dish at four feet with no mask with scarce amounts still managing to get on the dish from six feet away.

But no matter the distance, the demonstration showed that a mask nearly completely blocked bacteria from landing on the plates.

Just under 64% of the U.S. population has received as least one dose of the vaccine, with state rates ranging from a high of approximately 77% in Vermont and Massachusetts and lows around 46% to 49% in Idaho, Wyoming, West Virginia and Mississippi.

This story was reported from Los Angeles. The Associated Press contributed.