(WTVO) — People might start to see more signs sand alerts about getting a flu vaccine now that it is officially fall, and health leaders are weighing in on the best time to get the shot.

The short answer is that it varies. Health officials said that every influenza season is different, depending on when it peaks and what the dominant strain of the virus is at the time.

Leaders with OSF Healthcare, however, suggested using the month of October to make a decision. They said that the flu vaccine is a good tool to stay healthy, but those with underlying health conditions should make it a priority.

“For the most part, when [the emergency department sees] someone come in with flu, we’re looking at a patient that’s older,” said Dr. Jason Kole, director of emergency department services. “We’re concerned about the complications of the flu developing into pneumonia or another serious illness.”

Kole said that, once someone gets the vaccine, they have some level of immune system response fairly quickly. It takes a few days to build up a more robust immunity, though.