More than 15,000 Philadelphia School District employees — 81% of the public school system’s staff — have been fully vaccinated against COVID-19, officials said Wednesday.

The 2,250 staff that remain unvaccinated are submitting to twice-weekly COVID-19 tests.

“We know that vaccines are an effective mitigation strategy to stem the spread of COVID-19, so I want to thank all staff who have chosen to get vaccinated,” Superintendent William R. Hite Jr. said in a statement. “The science is clear that vaccines provide another layer of protection for all of us and our staff are doing their part to protect the health and wellbeing of themselves, the students we serve, and everyone who enters our schools and offices.”

Joyce Wilkerson, school board president, said she was pleased with the vaccination rate.

“It is the board’s duty to protect our children, many of whom cannot get vaccinated, and being vaccinated is the best protection against the virus,” Wilkerson said. “We believe that preventing COVID-19 infections through vaccines will lead to fewer missed school days, more in-person learning days, and ultimately, to improved student achievement.”

The school board approved a vaccine mandate in August; staff had until Sept. 30 to become fully vaccinated and submit evidence of their inoculation to the district.

In addition to being required to undergo testing twice a week, unvaccinated staff lost access to the bank of 10 days of quarantine leave that vaccinated staff receive if they are exposed to the virus.

Staff hired before Oct. 1 did not have to be vaccinated; all employees hired after Oct. 1 must be fully vaccinated.