At an afternoon news conference, the Democrat said plans were being made to bring in-person learning back as quickly as possible if the infection rate drops, though he cautioned that the bar to return would be higher than it was to close down.

“We’re going to fight this back. This is a setback but it’s a setback we will overcome,” de Blasio said.

Department of Education Chancellor Richard Carranza stressed that school would still be in session remotely.

The city had said since summer that school buildings would close if 3% of all the coronavirus tests performed citywide over a seven-day period came back positive. As the rate neared that point last week, de Blasio advised parents to prepare for a possible shutdown.

The mayor said the rate equaled that mark as of Tuesday.

The city’s more than 1 million public school students will now be taught entirely online, as most already are. As of the end of October, only about 25% of students had gone to class in school this fall, far fewer than officials had expected.

In-person school resumed Sept. 21 for pre-kindergarteners and some special education students. Elementary schools opened Sept. 29 and high schools Oct. 1.

At the time, the seven-day positive test average rate was under 2%.