As Boston prepares for its annual First Night celebration, city officials are urging New Year's Eve revelers to be cautious amid spiking levels of multiple infectious viruses.

“It's really not just COVID this season,” Mayor Michelle Wu said at a news conference Wednesday focused on safety precautions ahead of the event. “... I think because we had been isolated so much over the last two years, there has now been a little bit of resurgence of the flu more intensely, [respiratory syncytial virus] and others.”

In addition to outdoor events including the parade, fireworks display and concerts in Copley Square, Wu said the city decided it was safe to resume a range of indoor programming, including music classes, performances and other family-friendly activities at the Boston Public Library, the Copley Place Mall and churches across the city.

“[We] encourage everyone to do what feels comfortable,” Wu said, “and masking indoors can certainly help protect against the spread.”

In the two weeks leading up to Christmas, COVID-19 levels increased 11% across Boston, and hospitalizations for the virus were up 72%, according to the latest data from the Boston Public Health Commission. Last week, BPHC officials warned residents of an “early and rapid rise” in cases of the flu and other respiratory viral infections, causing “increased strain on Boston’s hospitals.”

“A happier and healthier and safer new year for everybody is a personal responsibility. Flu and COVID are still out there, still kind of circulating and peaking, and it’s affecting everybody,” Boston EMS Chief James Hooley said at Wednesday’s press conference. “If you feel great now, good. If you start to feel like you maybe get a little symptomatic around New Year's, maybe that's the time to stay home, stream something on TV or whatever. Maybe just don't put yourself out in a crowded situation if you're not feeling well and you think you could be a source of infection for others.”

Indoor events may have capacity limits and will be open to the public on a first-come, first-served basis, according to the First Night Boston website. The bulk of the celebration’s events will be staged outdoors, despite a rainy forecast.

“One of the best parts of this event is that it truly allows us to utilize so many outdoor spaces across the city and reminds us that we can lean into being a city that enjoys clear seasons,” Wu said. “And so in this winter season, we know Bostonians are hearty and prepared and have all the gear to be able to be outside and enjoy the ability to be outside.”

Additional transit police officers will be dispatched throughout the MBTA system during the festivities, MBTA transit police chief Kenneth Green said Wednesday, adding that there are no known threats, “credible or otherwise,” to the MBTA or to the event.

“I want to remind everyone that the First Night celebration is a family-oriented event,” Green said. “We ask our riders to act responsibly and be respectful to one another, and especially mindful of those with children, the elderly and people with disabilities.”

MBTA buses, trains and the commuter rail will increase service at 3 p.m. on Saturday and will be free to passengers starting at 8 p.m. until the end of service, which will be extended until 2 a.m. on Sunday.

First Night Boston events begin on Saturday at 10 a.m. and continue with an additional hour of programming on Sunday, including another fireworks display along the Boston Long Wharf harbor.

“Much has been said about the safety, but I’d like to emphasize a couple of things: it’s free, all over Boston ... and it’s family-friendly,” said Dusty Rhodes, an event organizer who has helped facilitate the last eight years of First Night Boston’s 48-year run.

When asked about her favorite aspect of the celebration, “between the ice skating, the ice sculptures, the pyrotechnics, the fireworks, the music, and the celebration of the city,” Rhodes said a personal highlight is seeing families ringing in the new year together. “I love to see all the families coming into town with the strollers and the little kids with all their little glitzy little lights up on their heads and just so much glee in their eyes.”