(CHICAGO) -- COVID-19 cases during the first week of the 2022-23 school year in Chicago Public Schools are much higher compared to the same time last year.
According to CPS data, 449 students have tested positive for the virus during the first week of the new school year -- 3.3 times higher than the 135 students who tested positive during the first week of the 2021-22 school year.
Additionally, 315 adults -- including people such as faculty and administrators -- have contracted COVID-19, CPS data shows. That's 4.8 times higher than the 65 adults who had COVID during the same period last year.
Doctors told ABC News it's not surprising more cases of the virus are cropping up compared to last school year for a couple of reasons.
One reason is because the BA.5 variant, an offshoot of the original omicron variant, is continuing to spread -- making up 90% of cases in the Midwest, according to the Centers for Disease Control and Prevention.
"Obviously COVID is still circulating in the community and the variant of COVID that is circulating, BA.5, is extremely transmissible, so that one person that's infected can infect a lot more individuals," Dr. Tina Tam, a professor of pediatrics at Feinberg School of Medicine of Northwestern University and a pediatric infectious diseases physician at Ann & Robert Lurie Children's Hospital of Chicago, told ABC News.
The second reason is because mitigation measures have been loosened.
During a media briefing earlier this month, the CDC said it was no longer recommending unvaccinated people quarantine after exposure, instead suggesting they mask up for 10 days and get tested five days after they were being exposed.
Following the news, CPS announced there would no longer be a requirement for students exposed to the virus to quarantine unless they test positive.
Additionally, masks continue to be optional for students and staff in school buildings and on school buses after CPS dropped its mask mandate in March.
Tan said some of these mitigation measures may need to be reinstated if COVID-19 cases continue to rise.
"If someone's exposed and they're not symptomatic, they can still go to school, but they should be wearing a mask," she said. "How many kids are actually doing that? I don't know. But I think that if the numbers continue to rise the way they're rising, one of the probably best things to consider is to put back into place a mask mandate."
The Chicago Teacher's Union said the increase in cases is concerning and, if infections continue to climb, it will demand that a mask mandate be reestablished.
"There is nothing stopping the district and we have advocated for this to immediately reimpose a mask mandate, if they are seeing spread," CTU vice president Jackson Potter told local affiliate ABC 7 Chicago.
The CTU did not immediately reply to ABC News' request for comment.
Tan said she also wants to encourage parents to vaccinate their kids, especially considering the low vaccination rate among students.
CPS data shows only about 51% of eligible students at district-runs schools are fully vaccinated against COVID-19.
The percentages vary widely depending on age. More than 63% of students aged 12 to 17 are fully vaccinated compared to a little more than 14% of children ages 4 and under.
"People just need to remember that COVID is still circulating in the community," Tan said. "Yes, this particular variant tends to cause mild disease. However, there are normal healthy children that will develop more severe disease with BA.5 and may be hospitalized from it."
She continued. "So, the best way to protect their children is to vaccinate them."