New York City's public schools, the largest school system in the United States with about 1.1 million students, will return to full-time in-person learning on Monday after the coronavirus pandemic forced children to learn remotely from crowded classrooms.

"All systems are go for a safe reopening", according to Mayor Bill de Blasio. "This is going to be one of those game-changer days, one of these days that we'll remember when we turn the corner on COVID," he said last week.

De Blasio believes that putting children back in the classroom will be the key to the city's resurgence and will help parents return to work.

The return to school comes as the Delta variant accounts for 98 percent of all positive COVID-19 samples tested in New York, according to the city.

New York Governor Kathy Hochul has directed the state's Health Department to institute a universal mask requirement in all schools, public and private.

"My number one priority is getting children back to school and protecting the environment so they can learn safely," she said.

At least 1,800 public schools in the city will hold in-person classes five days a week. Only children with weakened immune systems or a chronic illness (about 1,300) will be eligible to work from home, de Blasio said.

All 148,000 employees of the city's Education Department will be required to receive at least one dose of a COVID-19 vaccine by Sept 27.

Meisha Porter, New York City schools' chancellor, said she expected compliance from school staff.

At least 63 percent of all the city's teachers are already vaccinated. Teachers who aren't vaccinated must have weekly testing for COVID-19. The mayor said last month that any educator who didn't comply with the vaccination or testing requirement would be suspended without pay.

But District Council 37, the city's largest public-employee union, with 125,000 members and 50,000 retirees, filed an unfair labor practices complaint on Aug 23 against the city over the mandate.

Executive Director Henry Garrido said in a statement: "While we strongly encourage our members to get vaccinated, we do not believe that the city has the legal authority to change the terms and conditions of employment without bargaining."

Michael Mulgrew, president of the United Federation of Teachers praised New York's school teachers' overall willingness to comply with vaccine and mask mandates. They will have to wear them on all school property and school buses. They can only be removed to eat.

"The city's plans for masking, ventilation, social distancing and testing protocols will help keep students and staff safe this year," he

said in a statement.

Safety protocols of the city's Education Department will mean that each day, students and staff must fill out a form that states, "they are not experiencing any symptoms of COVID-19, have not recently tested positive, and are not currently required to quarantine based".

All classrooms will be required to have two air filters. They will also have hand sanitizers.

At least 61 percent of New York City's children aged 12 and over have been vaccinated. There is no vaccine mandate for children under 12 as they aren't yet eligible for vaccination.

Hochul said New York City has received $251 million in federal funding to initiate COVID-19 testing in schools and the state has received a total of $585 million in federal funding to support testing programs.

The city plans to issue a COVID-19 test to a random sample of 10 percent of unvaccinated people in schools twice a month. Vaccinated students and staff won't participate.

All children in elementary school will be tested for COVID-19 with their parents' consent. Unvaccinated middle and high school students will also be tested.

If someone tests positive, only unvaccinated students in close proximity to them will be required to undergo quarantine for 10 days to limit school closures. If they test negative within five days, they can stop quarantining early.

If the virus spreads in a school building it will be required to close for 10 days only if there is widespread transmission. Principals must ensure that children stay three feet apart where possible.

Michael Cordiello, president of the union which represents more than half of school bus drivers, warned that there was a worker shortage due to coronavirus and many drivers retiring. But the Education Department said the city will have enough school bus drivers when school starts.