New York City has issued a health advisory that recommends all residents wear a mask indoors and in public settings, in response to the emergence of the omicron variant. Officials said the new advisory strengthens the city's position on mask-wearing, though it echoes a previous recommendation issued in August.

Mayor Bill de Blasio and city health commissioner Dr. Dave Chokshi said the new variant had not been detected yet in the five boroughs, but it has ignited fears of worsening an ongoing surge in cases.

Monday's advisory, which Chokshi announced, falls short of a full mask mandate. De Blasio has repeatedly said he is opposed to reinstating all-encompassing mask mandates because he wants to focus on vaccinations. Previously, amid the surge in delta variant cases in August, the city also advised all residents to wear masks indoors -- without releasing a full mandate.

"Vaccination is the crucial strategy," de Blasio told reporters on Monday. He said he viewed the new advisory as a reminder of the danger posed by omicron as well as an increase in cases attributed to colder weather.

Currently, New York City residents are not required to wear a mask indoors except in schools and on public transit. Chokshi said the delta variant is presently driving the vast majority of new COVID-19 cases in New York City. He added that unvaccinated individuals are seven times more likely to be infected than those who are fully vaccinated.

"We want to deliver a very clear and unequivocal message that everyone should be masking indoors, regardless of their vaccination status," Chokshi said.

In addition to the mask advisory, de Blasio also expanded the city's vaccine mandate for public educators to roughly 102,000 employees of childcare and early intervention programs.

Mayor-elect Eric Adams praised de Blasio and South African scientists for their response to the new variant. He stressed the importance of working with Gov. Kathy Hochul, who declared a state of emergency over the weekend to boost staffing at health care facilities.

"Vaccination is our most important weapon, but coordination is second to that," Adams said.

Adams said he had recently received his booster shot. He urged other vaccinated New Yorkers to do so as well and for the unvaccinated to get their first shots.