Five cases of measles have been identified in Niagara, and more cases are expected.
Measles infections in Canada have surged to 227 confirmed cases since the start of this year, surpassing the total for all of last year.
Two people, including a child, have died in the U.S. following outbreaks there.
The last measles death in Ontario, was a child in Hamilton last year.
Medical Director of Infection Prevention and Control at Niagara Health, Dr. Karim Ali, tells CKTB, measles is serious in unvaccinated people.
The MMR vaccine is given as a two-dose series, the first dose at 12-15 months of age, and the second dose between 4 and 6 years of age.
He says the vaccine is very effective.
"None of these hospitalizations are in vaccinated people. In Canada, measles was considered eradicated in 1998."
Ontario began offering the measles vaccine as part of its routine childhood immunization program in the early 1970s, with a single-dose schedule, and introduced a two-dose schedule in 1996.
Dr. Ali says the vaccine is not linked to autism, and parents should not be concerned about misinformation they may have heard online.
"There is a high rate of complication, almost 10-15 percent are hospitalized. People need to know this isn't a benign disease, there are long-lasting complications in children."