New York City is making major expansions to its "Key to NYC" program, announcing a "first-in-nation" vaccination mandate for all private-sector workers and customers at indoor dining, fitness, and entertainment and performance venues effective Dec. 27.

The program is also expanding to require children aged 5-11 to show proof of one vaccination to enter those venues as well as high-risk extracurricular activities, such as sports, band, orchestra, and dance, by Dec. 14. Moreover, New York venues will require all patrons 12 and older to show proof of two vaccine doses, instead of just the initial dose of either Pfizer (PFE  )-BioNTech (BNTX  ) and Moderna (MRNA  ) vaccines, expect for those who have received the Johnson & Johnson (JNJ  ) one-shot vaccine.

"New York City will not give a single inch in the fight against COVID-19. Vaccination in the way out of this pandemic, and these are bold, first-in-the-nation measures to encourage New yorkers to keep themselves and their communities safe," said Mayor Bill de Blasio in a press statement. "From workplace mandates, to $100 incentives, to mobile and at-home vaccination offerings, no place in the nation has done more to end the COVID era."

De Blasio's decision comes as public health officials grow more concerned about the new, highly mutated Omicron variant and its potential impact as more people hold indoor gathering during the colder months. Currently, the Delta variant is the most pervasive variant in the United States, causing about 100,000 cases per day, according to data compiled by the U.S. Centers for Disease Control and Prevention.

The City plans to issue additional guidance on the new vaccine mandate later this month, as well as additional resources to support small businesses. According to the Mayor's office, 94% of NYC's public workforce is vaccinated.

New York City has administered over 12.5 million vaccination doses, according to the Mayor's office, with 89% of adults and more than 125,000 children aged 5-11 receiving at least one vaccine dose.