The Centers for Disease Control on Tuesday updated its mask guidance, telling vaccinated Americans in parts of the country with high COVID-19 caseloads that they, too, should wear masks indoors. The change came as the delta variant continued to drive an increase in cases in the United States that public health experts have watched with alarm.

The recommendation was a change from the agency’s statement in May that fully vaccinated people did not need to wear masks.

In for Jim Braude on Greater Boston, Sue O’Connell was joined by Dr. Sabrina Assoumou, an infectious disease physician at Boston Medical Center, and Nancy Krieger, a professor of social epidemiology at Harvard T.H. Chan School of Public Health.

Krieger said that it was key that vaccine access and administration continue to improve across the country so that everyone — those receiving the vaccine and those who can’t or won’t — can be better protected.

“Not everyone has equal access to conditions that enable them to get vaccinated,” said Krieger. “To assume that this is all voluntary recreational behavior and recreational mask wearing isn’t correct.”

WATCH: Experts on the guidance and mandates for masks and vaccines