With flu season upon us, the annual Quebec influenza vaccination campaign began on Monday.

In 2015, more than two million shots were administered.

As the goal of the campaign is to prevent complications, hospitalizations and death in high-risk groups, the vaccine will be free to children under two-years-old, pregnant women in their second or third trimesters, people with a chronic illness, health workers and people over the age of 60.

Montreal Public Health officer Renee Pare stressed the importance of getting the shot early.

"The flu will start in December and January, so we have time to get our flu shot in November," she said.

In the past, there has been confusing information about the efficacy of the vaccine. That has made rolling out the annual campaign a challenge said Caroline Quach, a specialist in infectious diseases at the MUHC.

"Some years, the vaccine doesn't work at all," she said. "We remember 2014-15, two years ago, was a complete disaster. What was in the vaccine was completely different from what was circulating and we saw efficacy at zero."

On average, the efficacy rate is 50 to 60 per cent. Health Minister Gaetan Barrette stressed the importance of getting the vaccine to preserve herd immunity for those who cannot receive it for health reasons.

"It's still beneficial to have the flu vaccine, especially for elderlies and immuno-compromised patients, but for others, it's a choice," he said.