A grocery store worker at Sobeys tested positive for hepatitis A, leading to the vaccination of more than 4400 people on Sunday, with vaccinations continuing over three days.
The Middlesex-London Health Unit set up four clinics to offer the free vaccine to concerned members of the public, reported the Kitchener-Waterloo Record.
Officials said those at risk included people who ate produce bought at the store since 11 August, but health officials have emphasised that it is highly unlikely that anyone might have contracted the disease by eating produce from the store where the infected employee worked. Vaccinations were available for those who felt they were at risk.
Hepatitis A is rarely serious. Symptoms include fever, fatigue, loss of appetite, nausea and jaundice.
Staff threw out produce and the whole store was disinfected. No other cases of the disease have been reported.