The new guidance from the CDC is quickly creating a ripple effect across the U.S.
Many states, major cities, schools and businesses are beginning to re-impose mask mandates as the delta variant causes a rise in cases.
Places like Nevada, Kansas City, Missouri, St. Louis and Atlanta are among the areas that have quickly re-introduced mask requirements for public indoor spaces.
In Kansas, the governor has ordered all state employees to wear masks indoors at work.
Washington state is recommending masks indoors again for people who are vaccinated.