Here’s why the CDC recommends wearing masks indoors even if you’ve been fully vaccinated against COVID-19

Vaccinated people need to mask up again, according to the U.S. Centers for Disease Control and Prevention. On July 27, 2021, the CDC recommended that everyone in areas with high COVID-19 infection rates wear masks in public indoor spaces, regardless of vaccination status.

It’s a reversal from the CDC’s May 2021 advice that the fully vaccinated could leave their masks at home and brought U.S. guidelines more in line with World Health Organization recommendations.

The Conversation asked Peter Chin-Hong, a physician who specializes in infectious diseases at the University of California, San Francisco, to help put into context the science behind the changing messages