TORONTO -- School-aged children now account for the highest share of COVID-19 cases of any demographic in Toronto but the city’s top doctor says that most infections are still being tied back to household transmission and not classroom outbreaks.

Medical Officer of Health Dr. Eileen de Villa said during a Board of Health meeting on Monday afternoon that the case rate among children ages four to 11 has steadily increased since schools reopened earlier this month and now stands at 64 per 100,000, up from 57 per 100,000 last week

De Villa said that the cohort, which roughly captures those school-aged children who are not eligible for vaccination, now accounts for more new COVID-19 cases per capita than any other age group for the first time since the start of the pandemic.

“It is important to note that at this point what we are seeing is the majority of cases in children to date are sporadic. We're seeing at this point that few are linked to outbreak. And in fact, what we do see is that the most common source of infection at this time amongst children is household transmission,” she said. “With that in mind it is absolutely key for parents to get vaccinated to help ensure the safe reopening of schools and the ability to provide ongoing in-person learning.”.

De Villa said that while there is limited data on the vaccination status of school-aged parents, one can use the 30 to 49 age group as a “reasonable proxy.”

She said that about 25 per cent of that age group is not fully vaccinated, suggesting there is “still some work that needs to be done.”

“Our data suggests about 190,000 (of that group) have not received a first dose,” she said. “It’s important for the board to recognize that it is absolutely key for parents to get vaccinated.”

De Villa’s comments on Monday afternoon come amid new data suggesting that more than a quarter of all known COVID-19 cases in the province are now associated with schools.

Up to 2 p.m. on Friday, the Ministry of Education says it was aware of another 135 COVID-19 cases; with 120 among public school children and 13 cases in education workers.

The associations of two other cases detected Friday were not disclosed.

There are now 1,450 known active cases of COVID-19 in schools across the province, and one school in Courtice, Ont. is closed.

At this point last school year, there were no more than 280 cases of COVID-19 found in Ontario schools, but that school year began approximately one week later, the more transmissible Delta and Alpha coronavirus variants were not present and vaccination was not yet possible.

COVID-19 cases tied to schools now make up 26 per cent of the province’s known active caseload.

Meanwhile, Toronto Public Health says it has formed a working group to plan the rollout and administration of COVID-19 vaccines to kids aged 5-11 once Health Canada gives final approval.

Pfizer says it plans to submit its COVID-19 vaccine trial data from children to the U.S. Food and Drug Administration in the next several days.

Toronto Public Health says the working group will be made up of “health partners, school boards, community representatives and the Ministry of Health.”

It estimates there are 200,000 children in that age group within Toronto.

Elsewhere in the Greater Toronto and Hamilton area (GTHA), school boards reported an additional 88 cases of COVID-19 detected between Friday and Monday morning.

There are now 711 cases of COVID-19 associated with schools in the GTHA.

CP24 counted at least 284 classes and cohorts ordered to move to online learning as of Monday, and the number is likely higher because large school boards such as Toronto District School Board and Toronto Catholic District School Board do not release statistics on classroom dismissals.