SAN FRANCISCO (KRON) — Flu season is upon us, and medical experts say the early signs show it may be a tough one. However, not everyone is signing up for flu shots and COVID vaccines — either postponing or just passing up getting both shots.

“Not only does it kill on average 30-35K Americans, but it hospitalizes 100 to 300k Americans a year, this is a serious infectious disease, much more serious than I think people appreciate,” said UC Berkeley’s Dr. John Swartzberg.

Swartzberg doles out data about the flu. While some seasons have been mild, this upcoming one doesn’t look so rosy.

“For one many didn’t have it last year, which means people don’t have immunity,” Swartzberg said. “Number 2, we found out that people in the Southern Hemisphere had a bad bought of flu, so those two things together and it could be a bad flu season. And that brings us to flu vaccines.”

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Data shows some are putting off getting that flu shot and sticking just to the latest COVID booster — thinking it might be too much for the body to manage all at once.

“It is understandable the concern, we have studied people who get flu and COVID, they may get a sore arm, but it is very little difference. So you do one and done, and it works out just fine. There is no increased risk of any serious side effects,” Swartzberg said.