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DENVER (KDVR) — What are side effects of the flu shot?

The flu is caused by several different strains of virus. Influenza A and B are the ones that spur flu season.

According to the Centers for Disease Control and Prevention, symptoms for both flu and COVID-19 can range from mild to severe, and both illnesses can cause fatigue, body aches, fever, chills, coughing or headache. Shortness of breath, runny nose and loss of taste or smell are more common with COVID-19.

The CDC recommends almost everyone 6 months and older get a flu shot by the end of October. For people with heart disease, the flu vaccine can lower the risk of dying from heart problems and any other cause, according to research published in March in the Journal of the American Heart Association.

Flu strains evolve, so the vaccines are reformulated every year. This year’s vaccines are designed to protect against the four flu viruses most likely to spread during the upcoming season.

If you’re planning on getting a flu vaccine, there’s a chance you could experience side effects. The CDC said the good news is that the side effects are generally mild and go away within a few days.

Here are the common side effects from the flu shot, according to the CDC:

  • Soreness, redness, and/or swelling from the shot
  • Headache
  • Fever
  • Nausea
  • Muscle aches
  • The flu shot, like other injections, can occasionally cause fainting.
  • The CDC also said that some studies have found a possible small association of injectable flu vaccine with Guillain-Barré syndrome

The CDC said that with any vaccine, you should watch for any unusual conditions, such as high fever, behavior changes, or signs of a severe allergic reaction after getting vaccinated.

Here are the signs of a severe allergic reaction, according to the CDC:

  • Difficulty breathing
  • Hoarseness or wheezing
  • Swelling around the eyes or lips
  • Hives
  • Paleness
  • Weakness
  • A fast heart beat or dizziness

Life-threatening allergic reactions to the flu shot are rare, the CDC said. If you’re experiencing a severe allergic reaction, the signs would most likely happen within a few minutes to a few hours after the vaccine is given.

Despite possible side effects, the CDC says the flu vaccine is “the first and best way to reduce your chances of getting the flu and spreading it to others.”

The Associated Press contributed to this report.