Niagara Region Public Health has declared an outbreak at Eastdale Secondary School in Welland.

The school has two cases of COVID-19 and has shut down five classes.

The first case was announced on Friday while the second case was announced on Sunday.

CBC contacted the District School Board of Niagara, but it did not immediately respond for comment.

This is the first local outbreak in a school and follows a string of local COVID-19 cases in schools.

It's unclear what kind of symptoms the infected people have or had, and how many people are isolating, but Dr. Mustafa Hirji, Niagara's chief medical officer of health, told CBC they can't rule out the virus infected both people at school, which caused public health to declare an outbreak.

"Fifteen percent of Niagara's population is either a student or staff person in a school and so you can roughly expect that 15 per cent of cases in Niagara would somehow be affiliated with a school," he explained.

"It was pretty much inevitable we would start to see cases. That works out to maybe one in every seven cases in Niagara will somehow be connected with a school, so when you start to think of the numbers that way, it's not that surprising we're already seeing cases."

Hirji said the number of daily cases in the Niagara region has increased from one new case to four new cases a day, which poses an increased risk for more school-related cases.

Despite that, he's not worried about schools closing as a whole, but said it will take a community effort to limit the spread of COVID-19 in the area.

He also predicts schools won't see large outbreaks like long-term care homes.

"In a long-term care home [or hospital] if you have an outbreak, the people who are part of that outbreak can't go anywhere. The patients are residents and have to stay there, the staff are needed to care for them so it creates a more difficult environment to control the spread where you really need everyone still there," Hirji said.

"With a school, because you can have people stop attending, we're able to have all the students and staff who might have been exposed to COVID-19 and are at risk of developing it, all leave the school so you don't leave any further risk for those who remain."

He said he understands families' concerns.

"Lots of parents are quite anxious and were calling public health today ... their anxiety is completely understandable."

Hirji said public health's phone line and live chat are open all day until 8:30 p.m., which means people can call throughout the day to avoid the surge of calls in the morning and subsequent long wait.