ROCKLIN (CBS13) — Just one week after the Rocklin Unified School District reopened for in-person learning, three students have tested positive for coronavirus.

Just nine days after returning to campus, the three Whitney High School students tested positive for the virus, forcing another 15 students and one teacher into quarantine.

“It’s obviously because more exposure and the chance of more people becoming infected,” parent Todd Milligin said.

The Placer County school falls under the state’s Red Tier, which allows individual school district boards to decide whether to continue in-person instruction or shift to distance learning after positive cases are reported.

On Tuesday night, Rocklin Unified voted to continue in-person learning with its current hybrid model until at least Jan. 8.

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“I think with the hybrid learning and continuing on with students going to school, it’s still going to have that risk of spreading and continuing on,” Milligin said.

In a statement, the district told CBS13, “The District is working with and receiving direction from the Placer County Public Health regarding health and safety protocols. Those who were in close contact will quarantine as per Public Health guidelines. Instruction to those students will continue through established distance learning models. In the meantime, our schools will remain open, following the state’s health and safety guidelines.”

Placer County health and safety guidelines require the three infected students to isolate for 10 days. A negative COVID test is not required before they return.

Those exposed must quarantine for 14 days and are encouraged to get tested before heading back to class.

Nearly 1,400 of Rocklin’s 13,000 students have opted to continue full distance learning.