It is one of a few regions in the country to mandate masks again.

“We’ve lost more than 500 St. Louisans to COVID-19, and if our region doesn’t work together to protect one another, we could see spikes that overwhelm our hospital and public health systems,” St. Louis acting health director Dr. Fredrick Echols said in a statement.

Masks will be required beginning on Monday in indoor public places and on public transportation, officials said, without elaborating. Masks will be strongly encouraged outdoors, especially in group settings, but not required. The rule will apply to people age 5 and older. By a federal order that runs through mid-September, masks already are required on all public transportation.

The decision already is stirring talk of opposition, both locally and at the state level, but many health officials back the move.