This week, some 720 flu cases were reported to Toronto Public Health, up from 469 the week before.
One reason for the increase is that the flu peaked earlier than usual, in early December, when kids were still in school.
"If we had a late-December peaking season, kids are out of school then and the virus tends to transmit less," Dr. Vinita Dubey said in an interview with CBC News.
Last year, nearly 32,000 people received flu shots at city clinics. But this time around, only 20,000 people have done the same.
To respond to the growing number of flu cases, the city has added five more flu clinics to the four that were already in place.
Click on the video above to see a full report from the CBC's Marivel Taruc.