All guests two years and older at Disney theme parks in the U.S. will once again be required to don face masks along with their optional mouse ears while indoors — a precaution against the spread of the highly infectious Delta variant of the coronavirus.

The new policy, announced on Disney's website, will be effective beginning Friday at Disney World in Orlando, Fla., and Disneyland in Anaheim, Calif. It includes a requirement for masks "in Disney buses, monorail and Disney Skyliner, regardless of vaccination status. This includes upon entering and throughout all attractions," the company says.

Face coverings in outdoor common areas remain optional, Disney says.

The policy says "Costume masks are not considered appropriate and are prohibited from being worn, in alignment with our existing rules."

The change comes weeks after Disney lifted a similar mandate and follows a change in guidance from the Centers for Disease Control and Prevention earlier this week. The CDC called on even fully vaccinated people to wear masks indoors if they live in places with "substantial" or "high" coronavirus transmission.

Since about the start of the month, both Florida and California have seen increases in coronavirus infections, according to data compiled by Johns Hopkins University.

Disney theme parks closed in March 2020 as the COVID-19 pandemic took hold in the U.S., but Disney World reopened last July with social distancing and mask requirements. California's Disneyland was reopened earlier this year, on April 30.

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