Many Americans are confused, some even outraged, about the Centers for Disease Control and Prevention’s new recommendations to return to mask-wearing. But while roughly half the U.S. population is vaccinated against the coronavirus, health officials are concerned about the rising numbers of new infections attributable to the highly transmissible delta variant — coupled with low vaccination rates in many areas of the country.

Furthermore, while the authorized coronavirus vaccines remain highly effective at preventing severe disease, hospitalizations and death from the delta variant, data suggests that fully vaccinated people with breakthrough infections — which are still considered rare — can spread the virus.

All of these factors mean masks remain an important tool in slowing the spread of the virus.

The CDC underscored that point by issuing a revised guidance on July 27 urging Americans, fully vaccinated or not, to mask up in public indoor spaces under certain circumstances.

Some people are catching coronavirus after being vaccinated. Johns Hopkins University infectious disease expert Lisa Maragakis gives advice on how to stay safe. (John Farrell/The Washington Post)

Below we’ve compiled answers to some of the most commonly asked questions surrounding masks and how to use them in this latest phase of pandemic life. These recommendations are drawn from CDC guidance, previously published Washington Post articles and new interviews with experts specializing in infectious diseases, public health and air quality.

Please keep in mind that as the coronavirus, its variants and vaccines continue to be studied and understood, masking advice is likely to change.