(Bloomberg) -- It’s not just Arkansas and Louisiana, where the delta variant has been raging, that are affected by the Centers for Disease Control and Prevention’s new recommendation for vaccinated people to mask indoors in some parts of the country. Most major U.S. urban areas also fall under the scope of the advisory.

CDC Director Rochelle Walensky told Americans Tuesday to consult the agency’s county-level map of transmission rates to determine whether they need to be masking indoors if they have already been inoculated against Covid-19. In locations with “high” or “substantial” transmission rates, it’s best if people mask indoors regardless of vaccination status, she said.

Those counties include all five of New York City’s boroughs, plus the counties that encompass Los Angeles, San Francisco, Houston, Dallas, Boston and Phoenix. The entire states of Arkansas, Florida and Louisiana are covered, along with most of Missouri, Mississippi, and Alabama.

Only a handful of the nation’s top cities have a low enough risk to go mask-free under the CDC’s guidance, including Chicago, Philadelphia and Washington. The county-level data is a sharp reminder that the Biden administration’s vaccination campaign is facing resistance not just from Republican-leaning states -- urban populations, including Black and Hispanic communities in some areas, are also lagging behind in many places.

©2021 Bloomberg L.P.