The announcement came Tuesday in reaction to rising hospitalizations across the country that include children.
Local leaders are banding together, as students prepare to head back to the books after holiday break.
Watch: Mayor De Blasio's Tuesday COVID-19 Briefing
"Schools need to be open, and so we are moving every day to make sure our schools remain safe," de Blasio said.
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Just as Adams takes the baton starting Jan. 3, the city will double the amount of PCR testing per week in each school, from 40,000 to 80,000, a move that will also include teachers and staff.
"Greatest sample size in each, so we get even more accurate and clear results. We are going to include both vaccinated and unvaccinated students," de Blasio said.
The city will also implement a new initiative called, "Stay Safe and Stay Open."
Before the break, COVID testing was limited to unvaccinated students whose parents turned in consent forms. That accounted for 330,000 kids, or about one-third of the entire school population. When they return, however, vaccinated students will be part of the testing, CBS2's Kevin Rincon reported.
"When there is a positive case in a classroom, every child takes home at-home test kits. Every child who tests negative comes back to school. It's as simple as that," de Blasio said.
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To make sure supply doesn't run out, Gov. Kathy Hochul said the state will give the city 2 million at home-tests kits.
"State and city working together. We are going to make sure that there is no shortage of supply," Hochul said.
"Your children are safer in school. The numbers speak for themselves," Adams added.
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"I don't know how you prepare for more and more staffing shortages, but it's something that has to be dealt with," Mulgrew said. "But it might mean that a school for a period of time might have to go remote."
Mulgrew thanked parents for their commitment to keeping kids in the classroom, but also asked for some help.
"Please, fill out the consent form. We want your child vaccinated, especially our 5-11-year-olds. That number is very low," Mulgrew said.
Watch Kevin Rincon's report
As CBS2's Lisa Rozner reports, in Paterson, New Jersey, students will be remote for the first two weeks of January. Before winter break, about 20% of school district employees were absent.
"We have to err on the side of caution at all times," Paterson Schools Superintendent Eileen Shafer said.
"I just felt like, here we go again," Paterson resident Tiffany Jacobs said.
Meanwhile, hospitalizations are climbing, especially among children. In New York City, pediatric COVID hospitalizations have almost quadrupled in the last two weeks. The Department of Health says none of those patients ages 5 to 11 were fully vaccinated.
"We all need to work together to keep kids in school and learning, and we can do that by vaccinating, boosting and masking up," said Dr. Tom Frieden, the former director of the Centers for Disease Control.
The agency has also shortened the recommended time for isolation after getting COVID, from 10 to five days if asymptomatic.
"The virus is adapting. Omicron is different, very different from prior strains and we need to adapt to do so appropriately the CDC is adapting their guidance," Frieden said.
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New Yorkers that spoke to CBS2 said they are embracing the change.
"I think it's very reasonable, I do, because we have to live with this for now on," said Marge Kelly of Chelsea.
"The science seems like it's there, so I'm pretty fine with it," said Mikey Cavenee of Hell's Kitchen.
Some are questioning if the change is a decision based more on science or economics, but CDC officials predict the U.S. still is not close to the peak of Omicron, so a plan needs to be in place to ensure society continues to function.
CBS2's Kevin Rincon and Lisa Rozner contributed to this report.
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