- The CDC updated its guidelines on Tuesday to recommend masks indoors, even for vaccinated people.
- The Delta variant makes it easier for vaccinated people to transmit the virus, the CDC said.
- Vaccinated and unvaccinated people infected with Delta may have similar viral loads.
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New science has once again prompted the Centers for Disease Control and Prevention to update its mask guidelines. The CDC recommended on Tuesday that fully vaccinated people wear masks in public indoor settings "in areas with substantial and high transmission." The agency specifically recommended that all teachers, staff, students, and visitors at K-12 schools mask up.
The goal of these new recommendations, CDC Director Rochelle Walensky said, is to "help prevent the spread of the Delta variant and protect others."
The CDC said in May that vaccinated people don't need masks, a recommendation based, in part, on data indicating that vaccinated people were less likely to transmit the virus to others.
But the Delta variant - now the dominant strain in the US - behaves differently than previous versions of the virus, Walensky said.
"Information on the Delta variant from several states and other countries indicates that, in rare occasions, some vaccinated people infected with the Delta variant after vaccination may be contagious and spread the virus to others," Walensky said on a Tuesday press call. "This new science is worrisome and unfortunately warrants an update to our recommendations."
Walensky said CDC investigations have even found that the amount of virus present in vaccinated people infected with Delta is similar to the levels found in unvaccinated people with Delta infections. That's an indication that vaccinated people can easily transmit the virus - even if they're less likely to get sick on the whole.
Still, Walensky added, "the vast majority of transmission, the vast majority of severe disease, hospitalization, and death, is almost exclusively happening among unvaccinated people."
The CDC estimated last week that unvaccinated people represent about 97% of hospitalized COVID-19 cases.
