CDC: Everyone should mask up indoors - whether they're fully vaccinated or not - as the Delta variant sweeps the US

• The CDC on Tuesday recommended that people wear masks indoors regardless of their vaccination status.
• Masks are important in areas with high coronavirus transmission and in schools, it said.
• The CDC had said in May that masks were no longer necessary for fully vaccinated people.

The Centers for Disease Control and Prevention is recommending that fully vaccinated people put their masks back on indoors, in some settings, as the more transmissible Delta variant spreads quickly across the US.

CDC Director Rochelle Walensky said on Tuesday that in areas of the country with substantial or high coronavirus transmission, vaccinated people should wear a mask in any public indoor setting.

"Some vaccinated people infected with the Delta variant after vaccination may be contagious and spread the virus to others," Walensky said, during a CDC press call Tuesday afternoon, saying that "new scientific data" on Delta has prompted the change.

The CDC also recommended that everyone in K-12 schools wear a mask indoors, regardless of their vaccination status, in line with recent recommendations from the American Academy of Pediatrics.

The CDC had said in May that fully vaccinated people largely did not need to wear a mask indoors. The new guidelines are designed to help prevent vaccinated people from spreading the highly transmissible Delta variant and to protect others from getting severely ill.

"Getting vaccinated continues to prevent severe illness, hospitalization, and death, even with Delta," Walensky added.

Delta spreads more easily, even among the vaccinated

The Delta variant, which is now responsible for most of the COVID-19 cases in the US, is the main reason for more vigilance even among vaccinated people.

Delta spreads faster and more easily than the earlier-detected versions of the coronavirus.

Scientists are finding that Delta grows more rapidly inside the body and that the viral load of an infected person with Delta tends to be about 1,000 times the viral load of the other strains of the virus.

This means even vaccinated people can contract and transmit the virus more easily. Their chance of landing in the hospital is still very low, though vaccinated people who have an increased risk of developing a more serious infection (older people and immunocompromised people, for example) may want to be more careful, experts say.

"What the Delta variant will do is that it will find any gap in our defenses," Dr. Hilary Babcock, an infectious-disease expert and the medical director of infection prevention at Barnes-Jewish and St. Louis Children's Hospitals in Missouri, recently told Insider.

"I don't think anyone is suggesting that Delta can, like, get through your mask better or get around your mask better," she added. "Masking and distancing still works for Delta. It's just that you have to be more meticulous."

'Children are not supposed to die'

Kids under 12, who can't get vaccinated in the US, are also at greater risk now of getting and spreading the virus.

Some doctors have raised concerns about more children being hospitalized with COVID-19, particularly in areas of the US with lower vaccination rates.

According to the CDC's tally, at least 409 children under age 16 have died from COVID-19 in the US; at least 281 of them were under 12.

"I think we fall into this flawed thinking of saying that only 400 of the 600,000 deaths from COVID-19 have been in children," Walensky said last week while testifying before a Senate committee. "Children are not supposed to die."

One of the most concerning COVID-19-related conditions that children can develop is multisystem inflammatory syndrome, or MIS-C, a rare malfunctioning of internal organs including the heart and lungs. MIS-C doesn't usually pop up until several weeks after a COVID-19 infection, but it can happen after both mild and severe cases. Left untreated, it can be deadly.

"We know how to actually have kids come back to the classroom and do it safely: ventilation, a reasonable amount of spacing, and strict mask use," Dr. Andrew Pavia, the chief of pediatric infectious diseases at the University of Utah, recently told Insider.

His state is one of at least eight (Arizona, Arkansas, Iowa, Oklahoma, South Carolina, Texas, Utah, and Vermont) where schools are barred from implementing mask mandates.