Shortly after returning to in-person learning at Century High School at the beginning of April, Joey Keillor's son Jon had to return home to quarantine. He had been exposed to a case of COVID-19.

Rochester's elementary students returned to the classroom in March, and secondary students returned in April. And since then, there has been a slight rise in recorded cases working their way through the School District. For the Keillors, that means Jon had to go into quarantine only a week and a half after finally being able to return to school.

"As a parent, of course, you understand they have to have some protocols, but it's just really frustrating to be in and out," Joey Keillor said.

ALSO READ: COVID cases inch up as Olmsted County sees vaccination numbers climb

According to Rochester Public Schools' COVID-19 dashboard, there were 22 new cases of COVID-19 from April 11-18. During that same time period, there were 411 students in quarantine, which is the highest number of people in quarantine since the district started the dashboard in October, representing about 2.3% of the total student population.

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From April 5-11, there were 32 new cases of COVID, which was the highest number of actual cases in one week since November. There were 262 students in quarantine during that period, representing about 1.4% of the student population.

In total, there have been 54 new cases since secondary students returned to school on April 5.

Heather Nessler, executive director of communications for the district, said although its unfortunate, the district isn't surprised by the increase in quarantine numbers.

"A lot of our secondary students have more chances for exposure because they're moving around the buildings," she said. "We knew this would probably happen just based on data, so we were kind of prepared for it. But, it's not what we want to see; we want our kids to be in school."

Prior to that, the numbers were a little lower, although they bounced around a bit. During the week of March 29-April 4, there were four new cases recorded in the district. The week of March 15-21, there were 19 new cases.

Graham Briggs, director of Olmsted County Public Health, said roughly a third of the cases they've identified over the past week have been in school-age children.

In addition to Rochester, several other area school districts routinely post their case numbers. As of Wednesday, Plainview-Elgin-Millville had no active cases among students or teachers. Byron Public Schools had 14 total positive cases, and 38 people in quarantine during the period of April 9-15.

Briggs said approximately 40% to 50% of the 16- and 17-year-olds in the county have been vaccinated against the virus. He also added that it's "quite possible" the age of eligibility for the vaccine could decrease again in the near future.

"I think we can say that we're seeing people under the age of 18 become more and more the drivers of community-level transmission," he said. "We're seeing an increase in kindergarten all the way up through 12th grade."