While most of Massachusetts shifted into Phase 4 of the state's reopening plan on Monday, Boston adopted a modified version with lower caps on most indoor and outdoor events.

"This is consistent with the cautious approach that we've taken throughout the pandemic," Mayor Walsh said during a City Hall press conference on March 19. "It's not a lot of changes but there are some changes that we are not going to be moving forward with as much as the state."

Instead of allowing up to 100 people to gather indoors and up to 150 people to gather outside, Walsh said Boston will only allow indoor gatherings of up to 60 people and outdoor gatherings of up to 100 people until the city's positive test rate stays below 2.75 percent for two consecutive weeks. For private residences, the gathering limits will remain at 25 people outside and 10 people inside.

The city's positivity rate is currently at 3.5 percent, the mayor said. The city's more stringent restrictions will not apply to indoor or outdoor stadiums, arenas or ballparks, meaning that Fenway Park and TD Garden will still be able to host fans up to 12 percent of their maximum capacity starting Monday, Walsh said.

He said the city will also wait for its positivity rate to stay below 2.75 percent for two weeks before allowing Fenway or TD Garden to increase the number of fans allowed at games.

"The case numbers have stayed below our thresholds of concern for about a month now. We are ready to move forward to reopening, so we're happy in the trend we're going. We're obviously not where we completely want to be, but we're getting to a better place," Walsh said. But he added: "The trend has been flat for several weeks. So, we did see a decline, but it's been flat for the last several weeks. So, we know that we still have work to do to make sure that we combat this virus."