They say anyone who drank juice from the Big Carrot between March 17 and April 2 may have been exposed to the virus, which can cause a potentially serious liver disease.
Toronto Public Health says the hepatitis A vaccine is most effective when received within two weeks of exposure.
It says symptoms typically appear between 15 and 50 days after exposure, although some who contract it may not show any sign of infection.
Symptoms include fever, fatigue, nausea, dark urine, stomach pains and jaundice.
A free vaccination clinic was also held Sunday.