EDMONTON -- An outbreak at an Edmonton school was "likely" caused by Alberta's first in-school transmission, Dr. Deena Hinshaw said Friday.

Two people from Waverley School tested positive on Thursday, the Edmonton Public School Board told CTV News. Approximately 12 students from a combined Grade 1 and 2 class and seven staff members are in self-isolation.

Hinshaw said the two people were at school while infectious, and that one of the cases "seems to have been the source for the other."

"It seems to be a likely explanation," Hinshaw said, and added it's possible more cases will come from the outbreak.

"This is not unexpected and not a cause for alarm."

EPSB said the school was thoroughly cleaned and will remain open.

As of Friday, Alberta Health Services had confirmed 78 cases of the coronavirus at 57 schools across the province.

Alberta reported 107 new cases of COVID-19 and one more death on Friday afternoon.