Fulton County Schools will require masks in schools located in areas with high COVID-19 case counts.

The state’s fourth-largest district initially said masks would be optional inside buildings and required on buses.

But on Monday, officials announced an update: Everyone must wear a mask in “schools located in municipalities where the rate of infection exceeds 100 per 100,000 residents.”

The district will determine which schools will mandate masks for Monday, Aug. 9, the first day of school, using numbers from the report issued by the Fulton County Board of Health later this week.

”We are currently experiencing a notable increase in the number of students and staff being diagnosed with COVID-19 amongst the vaccinated and unvaccinated,” the district said in a statement.

“This also includes an increase in the number of school-age children and staff members requiring hospitalization. Data indicates the delta variant is much more contagious and more severe for unvaccinated persons.”

The district will track case counts using data from the health agency, which issues a report once a week on Wednesdays. The school district will post a list of the schools where masks are required.

As of the most recent report, seven Fulton County cities served by the district have rates that exceed the threshold, according to district spokesman Brian Noyes. They are: College Park, East Point, Fairburn, Hapeville, Palmetto, South Fulton and Union City.

Atlanta’s incidence rate also is over the mark, but students in that city attend Atlanta Public Schools. APS is requiring masks in all buildings and starts school Thursday.

The Fulton district also will require masks in any school located in a jurisdiction that mandates masks in public spaces.