In a low-key COVID-19 briefing that will likely be his last before Christmas, Mayor Marty Walsh urged Bostonians to contain the virus’s spread by exercising caution as they celebrate the winter holidays.

“You should only celebrate only with the people that you live with,” Walsh said, echoing advice from Gov. Charlie Baker and others.

“I know that it’s tempting, and it’s been a difficult year for a lot of people, and you want to bring other folks into your household,” Walsh said. “But that’s not safe for you, that’s not safe for them, that’s not safe for the people you might come into contact with.”

“Getting tested does not protect you from this infection,” he added. “You cannot test your way in or out of safe traditional gathering this year.”

For some people, Walsh acknowledged, refraining from gatherings with family and friends may be especially difficult as 2020 draws to a close.

“Many of you have had to make lots of sacrifices — sacrifices that you could never imagine this time last year,” Walsh said. “It’s okay to be overwhelmed; it’s okay to be tired; it’s okay to be sad. Don’t be afraid to talk to somebody.”

Individuals who feel they need help can speak with a healthcare provider or community organization like the Samaritans, who can be reached at 877-870-4673, Walsh said. They can also call the city’s 311 helpline.

“We have the ability to connect you to resources,” Walsh said. “I think that you need to take that opportunity if that’s the case.”

The mayor also reminded the public that the city is currently in a modified version of phase II, step 2 of reopening, with museums, movie theaters and gyms closed until at least Jan. 6. Boston’s community positivity rate has risen to 8.8%, up from 7.2% last week, Walsh said.

In response to a reporter’s question, Walsh said he doesn’t know if the Boston Police Department is currently investigating troubling comments — revealed last week by The Appeal — made by officers during a racial-justice protest on May 31 and June 1.

“There could be investigations going on right now,” Walsh said. “I have not had that conversation with the commissioner.”

The behavior described by The Appeal, in theory, could be investigated by Boston’s new police civilian-review board as well as the department’s internal-affairs unit, Walsh said.

The mayor also had a word of warning about holiday weather, saying rain and relatively high temperatures could bring flooding and re-freezing the coming days — with any still-unshoveled snow exacerbating the situation.

“We’re asking people, as much water as we can get off the street, it’d be great to do that,” Walsh said.

Despite the press conference’s muted tone, Walsh struck a guardedly optimistic note as he looked toward 2021.

“We are finally at the point where we feel like we have less days ahead of us of this virus than we do behind us,” he said. “And while we don’t know exactly when this pandemic will end, we do know that there are better days coming."