NEW YORK — A COVID-19 vaccination requirement for teachers and other staff members took effect in New York City’s sprawling public school system Monday in a key test of the employee vaccination mandates now being rolled out across the country.

Mayor Bill de Blasio said 95% of the city’s roughly 148,000 public school staffers had received at least one vaccine dose as of Monday morning, including 96% of teachers and 99% of principals.

Some 43,000 doses have been administered since the mandate was announced Aug. 23, de Blasio said.

“Our parents need to know their kids will be safe,” the mayor said. “They entrust us with their children. That’s what this mandate is all about. Every adult in our schools is now vaccinated, and that’s going to be the rule going forward.”

U.S. Secretary of Education Miguel Cardona joined de Blasio’s virtual briefing and hailed the vaccine mandate.