There have been 342 confirmed cases of the flu so far this season.

That is more than double the number of cases compared to last year.

“We've seen some shift in the virus,” said Chief Medical Officer of Health Dr. Charles Gardner. “The match for this particular strain isn't as good as we'd like it to be. We might not get as good protection from the vaccine.”

Influenza A is known as a more serious form, and can hit seniors particularly hard.

In Toronto, 110 people have contracted the flu and another 42 in York Region.

“You can go from walking well to being really, really sick within a matter of days,” said York Region’s Manager of Communicable Diseases Joy Marshall. “I think people underestimate how sick you truly are. This is not a common cold...this is influenza.”

Health officials in Simcoe County and Muskoka have seen only 15 cases, but are prepared if that number spikes.

They say the best way to stay healthy is to get your flu shot, and wash your hands often.