The Los Angeles Unified School District will require all students over the age of 12 to get vaccinated against COVID-19. School officials said that students will have until January 10 to provide proof they are fully vaccinated. Students who are not vaccinated will not be allowed to return to school after winter break.

Students involved in in-person extracurricular activities will have to get vaccinated no later than October 31.

For students who turn 12 during the school year, they will have 30 days to get their first shot and two months to get the second dose.

The policy will apply to roughly 225,000 students in the district. District officials estimated that about 80,000 students have not yet been vaccinated.

“We’ve always approached safety with a multilayered approach: masks, air filtration, and coronavirus screening,” Interim Superintendant Megan K. Reilly told The Los Angeles Times. “But we are seeing without a doubt that the vaccines are one of the clearest pathways to protecting individuals from getting severe sickness as well as for mitigating transmission of the COVID virus. It is one of the best preventive measures that we have at our disposal to create a safe environment at schools.”

Since the start of the school year, officials said that over 5,000 students have tested positive for COVID-19.

The district, which has over 600,000 students, is the largest in the country to mandate vaccines for students. The Culver City Unified School District, which serves 7,000 students, approved a vaccine mandate for students last month. Over a dozen other school districts in California are considering similar mandates.

Officials did not say if they would expand the mandate once a vaccine is approved for children under the age of 12.