A vaccination clinic was set up at a Toronto daycare on Monday, after it was discovered that an adult who contracted the virus had dropped off and picked up a child at the facility on two occasions last month.

On Monday, dozens of children and parents were vaccinated at the West End YMCA Daycare at 931 College St.

Over the weekend, parents had learned about the adult who had been at the daycare and the fact that their children may have been exposed to measles. The notification came via Toronto Public Health.

While Toronto Public Health wouldn't provide specific details on the case on Monday, officials did confirm the exposure at the daycare.

"The staff, children and parents were exposed to a case of measles," Dr. Vinita Dubey of Toronto Public Health told CBC News on Monday.

A vaccination clinic was set up at a Toronto daycare on Monday, after health officials learned that an adult who developed measles dropped off and picked up a child at the same facility in late January. (CBC)

A parent told CBC News that the adult was at the daycare on two occasions during the week of Jan. 26.

Children are typically first vaccinated for measles at the age of 12 months, but are not vaccinated again until they are four to six years old. That suggests some children at the daycare may have only received a single vaccination to date.

Samantha Mangano, who was at the College Street daycare on Monday morning with her son, said she thinks Toronto Public Health has done their due diligence, but that she wishes "it would have been posted on the door when the exposure was noted with the daycare."

'Incredibly contagious'

Dr. Michael Gardam, an infectious disease specialist, said that anyone who has had a single vaccination and is then exposed to measles should get a second vaccination dose as quickly as possible.

Dr. Michael Gardam says measles is "one of the most contagious infectious diseases we know." (CBC)

Within 72 hours of exposure is the ideal window in which to receive a second vaccination.

But Gardam said a second vaccination will still have benefits should a person have a subsequent exposure to the virus.

Gardam said measles is highly contagious.

"Measles is one of the most contagious infectious diseases we know, so literally walking in the room, spending three minutes and picking up your child is enough to potentially infect the entire room. It would all depend on whether they actually have protective antibodies or not," Gardam told CBC News in an interview on Sunday.

"So, it is really incredibly contagious and it's spread through the airborne route. So I don't have to touch you, or come even close to you — if you're breathing the air that I just exhaled, you can get infected."

Health officials have recently confirmed six cases of measles in Toronto — four adults and two children under the age of two.