(ABC4) – On Tuesday, the Centers for Disease Control and Prevention issued new masking guidelines, even for vaccinated people, in response to new information about the ability of the Delta variant to spread.

In addition to recommending masks inside for teachers, staff, students, and visitors to schools – regardless of vaccination status – the CDC has recommended that anyone living in areas of “substantial and high” virus transmission wear a mask inside.

Most new infections in the U.S. continue to be among unvaccinated people. But “breakthrough” infections, which generally cause milder illness, can occur in vaccinated people. When earlier strains of the virus predominated, infected vaccinated people were found to have low levels of virus and were deemed unlikely to spread the virus much, CDC Director Dr. Rochelle Walensky said.

But with the Delta variant, the level of virus in infected vaccinated people is “indistinguishable” from the level of virus in the noses and throats of unvaccinated people, Walensky said.

The data emerged over the last couple of days from 100 samples. It is unpublished, and the CDC has not released it. But “it is concerning enough that we feel like we have to act,” Walensky said.

Vaccinated people “have the potential to spread that virus to others,” she said.

So where should you put your mask back on?

According to the CDC’s COVID Data Tracker, the majority of counties across the U.S. are seeing substantial or high COVID-19 transmission. Southern states like Louisiana, Florida, and Arkansas are entirely red, meaning they are in the ‘high’ level, as of Wednesday.

Various counties across the Western States, including Utah, are within the substantial or high level.

States across the Midwest and in the Northeast largely have more yellow counties – moderate transmission – while Plain states like North Dakota, South Dakota, and Nebraska have mostly blue – low transmission – counties.

Below is the CDC’s COVID Data Tracker map as of Wednesday.

CDC COVID Data Tracker, Mon. July 19-Sun., July 25 (CDC)

As you can see, Utah is among those states seeing mostly high transmission levels.

Of the state’s 29 counties, only seven are not in the high transmission category – Morgan, Summit, Rich, Daggett, Sevier, Piute, and Wayne. Even among those seven counties, Morgan and Summit still fall within the substantial transmission category.

Based on the latest CDC guidance, this means everyone, vaccinated or not, should be wearing a mask when indoors in all but five counties.

Here is a closer look at Utah’s COVID-19 transmission rates, courtesy of the CDC.

Only 46% of Utah’s 3.2 million residents are fully vaccinated against the virus. Today the CDC also recommended masks for all students, teachers, and staff in K-12 schools. The vaccine is not currently available for kids 11 and under.

“Once all school-age kids have access to the vaccine, we won’t need to recommend universal masking for unvaccinated individuals,” Dr. Angela Dunn, Executive Director of the Salt Lake County Health Department says. “But right now, it is our collective responsibility to protect those who don’t even have the option of getting vaccinated.”

Dr. Taki May of Intermountain Healthcare also expressed concern.

“I am worried about the kids going back to school with the vaccine not being available to them because they’re not great at hand hygiene, they like to share things including germs,” Dr. May explains. “I think it’s a good idea to have kids masked.”

For more on COVID-19 in Utah, click here.