To prevent further spread of the Delta variant, the US Centers for Disease Control and Prevention updated its mask guidance on Tuesday to recommend that fully vaccinated people wear masks indoors when in areas with "substantial" and "high" transmission of Covid-19, which includes nearly two-thirds of all US counties. This includes schools. The CDC recommends that everyone in grade schools wear masks indoors, including teachers, staff, students and visitors, regardless of vaccination status.
The CDC defines “substantial transmission” as counties that have 50 to 100 cases per 100,000 residents over a seven-day period and “high transmission” is more than 100 cases per 100,000 people over seven days.
"In recent days I have seen new scientific data from recent outbreak investigations showing that the Delta variant behaves uniquely differently from past strains of the virus that cause Covid-19," CDC Director Dr. Rochelle Walensky said on Tuesday. Federal health officials still believe fully vaccinated individuals represent a very small amount of transmission. Still, some vaccinated people could be carrying higher levels of the virus than previously understood and potentially transmit it to others.
Two factors that led to this decision: the prevalence of the Delta variant and low vaccine uptake. When the CDC previously revised its guidance on May 13 for vaccinated people to unmask, Delta only represented 1% of reported infections. Now, according to the CDC, it represents at least 83% of cases.
The CDC’s guidance is only a recommendation, leaving it up to states and local officials on whether to reintroduce their mask rules for certain people. NYC, Nassau and Suffolk currently are listed as areas of "substantial transmission."