It may not seem like time yet to get your flu shot, but it is.

“We do think about flu season being in the winter,” said Dr. Jared Pehrson with MedExpress. “It actually starts in the early fall and can go all the way into the early spring.”

The flu shot doesn’t always cover the same strains of influenza.

“The experts are always looking at recent years,” said Pehrson. “They’re looking at the other side of the globe, the other hemisphere, which strains were circulating there. They’re always trying to guess which ones are going to be the predominate strain circulating.”

Even if it isn’t a perfect match, having the flu shot can reduce your symptoms, because all the strains have some parts in common.

“They cause the respiratory flu, which is like the mother of all colds,” said Pehrson. “Basically cold symptoms like runny nose, congestion, cough, sore throat, but it comes on quick and hard compared to a cold. It’s generally more severe, with high fevers, body aches, just generally feeling awful.”

That’s different from the so called stomach flu, or gastroenteritis, which is marked by watery diarrhea, abdominal cramps, nausea or vomiting, and sometimes fever. The flu shot does not protect against that.