As of Monday, all New York City public school staff are required to have their first dose of the COVID-19 vaccine, prompting a substantial increase in vaccinations among educators. Officials said 18,000 staff members got vaccinated over the past 10 days.

Now, 95% of the education department’s roughly 148,000 employees have received at least one shot.

The city saw a similar spike in vaccinations after the mandate for health care workers went into effect last week. At a morning press conference, Mayor Bill de Blasio urged the nation’s governors and mayors to follow suit. “Put these mandates in place,” he said. “They work.” U.S. Secretary of Education Miguel Cardona briefly joined the press conference to praise the city’s vaccine requirement. “You’re doing it right,” he said.

Many parents have cheered the vaccine mandate, saying it makes them feel much safer about sending their children to school. “It means there is an actual bubble of safety around our children,” Schools Chancellor Meisha Porter said.

But the mandate is also causing some upheaval. There are still thousands of education department employees who are not vaccinated and are barred from coming into buildings. For weeks, administrators have warned of staffing shortages. On Monday, thousands of substitutes and central office staff were deployed to classrooms. Multiple administrators said they were able to staff their schools with minimal disruption. But the scramble to cover classes also led to teachers teaching subjects, grades and groups outside their licenses.

Jenny Ottinger, an instructional coordinator in the Bronx who coaches 3K and pre-k teachers, was redeployed to a seventh grade special education classroom where she was supposed to teach math. But she said she is not certified for special education or math.

“It didn’t go ideally for the children,” she said, noting that a fight broke out between students at one point. “All teachers should be vaccinated but they should have a qualified person in place [to replace those who are not]. Kids need a lot of stability, particularly after a year of not being in the classroom.”

“I’m not happy with the implementation even though I agree with the goal,” Ottinger said.

One parent, who asked to remain anonymous, said his kindergartner with autism was placed with a new teacher this morning, and then switched to another class a few hours later. He said he is now working with a nonprofit to identify private school options for his child. “It is unsettling that schools cannot get the support they need especially for special needs children. Placing unlicensed staff in classrooms with children [with] severe needs is not only dangerous but completely negligent,” he said.

Mayor de Blasio has said repeatedly there were thousands of substitutes ready to go — as many as 9,000 teachers and 5,000 paraprofessionals — and the city plans to pay them extra to entice them to take the positions. But several principals told WNYC/Gothamist they have had trouble securing subs even before the vaccine mandate went into effect.

Principals have also been sounding the alarms about a shortage of non-instructional staff, including school safety agents and cafeteria workers who have had lower vaccination rates. As of Monday, about 84% of school safety agents had gotten a shot, but schools that usually have multiple safety agents on duty may have fewer today. Still, Porter said the education department has ensured that all schools have security in place. “We pulled staff members who were not working in school buildings into school buildings,” she said.

More than 500 employees received medical or religious accommodations, meaning they will continue to be paid but have to work outside the school. Other employees who don’t get vaccinated have to take unpaid leave — and can keep their health insurance — or they can resign. Mayor de Blasio has said he’s not eager to fire people, he wants them to get vaccinated, and when they do, they can return to their jobs.

Schools were instructed to have staff at the door with a list of workers who can’t come in, although if those employees got vaccinated over the weekend and showed proof, they could enter the building. “Folks are showing up with vaccine cards this morning,” Porter said. Pointing to the impact of mandates elsewhere, de Blasio said he also expects more staff to get shots and return to work soon.

This is a developing story and will be updated.