Coupled with the emergence of new viral threats in recent weeks, the possibility of a spike in Covid cases over the coming holidays has brought proponents of school lockdowns out of the woodwork to warn parents that the country may not be done with disruptive pandemic-related restrictions.

These warnings come despite new research showing the devastating impact of prolonged closures on schools and their pupils across the country.

A study this week from the American Enterprise Institute found that parents “punished” public schools with longer durations of remote instruction by taking their business elsewhere during and after the pandemic. 

Public school enrollment fell nearly universally in the 2020-21 school year, the report said, but schools that moved quickly to return to in-person instruction began rebounding in the 2021-22 school year.

School districts that were fully hybrid and frequently mandated remote instruction saw additional declines in enrollment in the 2021-2022 school year. The study estimates that the school districts with the longest duration of remote instruction lost a total of 500,000 students due to their pandemic policies.

While complete data for the 2022-23 school year that began in September is not yet available, major cities including New York, Chicago, and Los Angeles all have reported further declines in enrollment this year versus last.

The closures negatively affected not only the quantity of students but also the quality of education. Federal data from the nation’s report card — the National Assessment of Educational Progress — showed a steep decline in math and reading abilities earlier this fall.

“It’s clear that Covid-19 shocked American education and stunted the academic growth of this age group of children,” the commissioner of the branch of the Department of Education that administers the assessment, Peggy Carr, said.

Despite the evidence of the harm caused by school closures, the head of the nation’s Covid response effort, Anthony Fauci, hinted over the weekend that remote instruction could be returning to schools in certain areas. Speaking on CBS’s “Face the Nation,” Dr. Fauci said he was “not sure” whether schools would reopen following a likely holiday infection spike.

“You have to balance, and you do it in real time depending upon the viral load of disease in your region,” Dr. Fauci told the show’s host, Margaret Brennan. “You have to have the local authorities evaluate on a situation-by-situation basis the potential collateral deleterious effects — the effects of what might happen if you have so many kids getting infected.”

Later that day, the director of the nation’s second-largest teachers union, Randi Weingarten, also expressed concern over rising viral infections. Ms. Weingarten was a prominent advocate of school closures in 2020.

“Our country is facing a tridemic: flu, RSV and COVID,” Ms. Weingarten tweeted, sharing an article about the collision of the three contagious viruses. 

Ms. Weingarten and others are concerned about a nationwide spike in respiratory syncytial virus, a common cold-like respiratory illness on top of seasonal flu and Covid, and are referring to the combination of infectious respiratory viruses as a “tridemic.”

Ms. Weingarten shared a statistic that three-quarters of pediatric hospital beds across the country are currently occupied, which some saw as an indication that the teachers unions — which widely supported earlier Covid lockdowns in the interest of protecting teachers’ health — may soon be agitating for another round of closures. 

On Monday night, however, Ms. Weingarten sought to reassure those people by saying on Twitter, “Personally I never want to see mass schools [sic] closures ever again.” She did not respond to a request for comment.

Covid-related hospitalizations have been steadily less than 50,000 persons per week since the Omicron surge last winter, according to data from the University of Washington. At the virus’s peak last winter, more than 160,000 persons were hospitalized.