SACRAMENTO (AP) — California schools that haven’t resumed in-person instruction will not be allowed to do so if the counties where they are located are moved to a more restrictive tier due to rising coronavirus cases, state officials said.

The state’s Department of Public Health said late Thursday K-12 schools can reopen in a county once it has been moved out of the most restrictive purple tier — which signals widespread virus transmission — for two weeks.

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But if schools haven’t resumed in-class instruction and the county returns to the most restrictive tier, they can’t do so, the agency said in an email.

That could happen to San Diego County, which has seen a recent rise in coronavirus cases tied to San Diego State University. The infections could push California’s second-most-populous county to the most restrictive tier when the state’s color-coded system for business reopenings is updated next week.

Some San Diego County schools have already resumed in-person classes and others don’t plan to anytime soon, but some districts had set campus return dates in late September and October.

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Paul Gothold, the county’s superintendent of schools, said in an email to school officials that the change could “punish schools and families that have been taking time to plan carefully for safe reopening.”

Under California’s reopening system, counties revert to a tier with more restrictions on activities if cases are above state-required thresholds for two straight weeks. The system is updated on Tuesdays.

California has seen an overall slowing of virus infections in recent weeks and a decline in hospitalizations. Gov. Gavin Newsom said he expects more counties to move to less restrictive tiers next week, but San Diego County has seen an increase — not a decrease — in infections.

San Diego State University has reported more than 700 virus cases in recent weeks, prompting the university to move classes online and mandate virus testing for students living on campus.

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Under certain conditions, schools can seek waivers to resume in-person instruction for elementary schools when the counties where they are located are in the purple tier. More than 50 schools in San Diego County obtained these waivers but the county stopped taking applications once schools were broadly allowed to open this month.