Winter is coming, and that means flu season. During the upcoming months, it's projected that between 157 million and 168 million doses of the injectable flu vaccine will be available for those hoping to avoid the worst of the flu strains, according to the Centers for Disease Control and Prevention.

An influenza vaccine is considered the best way to reduce your chances of getting the bug, and the CDC recommends that everyone 6 months of age and older receive one every year. It’s no surprise that vaccines can cause side effects, and for the flu shot they’re generally mild. Because the virus and vaccines slightly vary every year, so do the potential reactions.

"Since the flu virus frequently drifts in its genetic composition, you have to reformat the vaccine, and this is one of the reason[s] that people have to [get a flu shot] on an annual basis," Dr. William Schaffner, a preventive medicine and infectious disease expert at the Vanderbilt University School of Medicine, told Live Science.

The most common side effect of vaccination was soreness at the vaccination site lasting less than two days, and, according to the CDC, 10 to 64 percent of patients experienced this reaction.

Other common side effects from the flu shot include headache, fever, nausea, and muscle aches. The flu shot can also occasionally cause fainting, just like other injections. Only about 1 to 2 percent of people who get a flu shot will have fever as a side effect, Schaffner told Live Science.

Rare but serious side effects — including allergic reactions — can occur. If you experience serious side effects, you should seek medical care immediately, the CDC says.

This year, the agency has also changed its recommendations for flu shots in people with severe egg allergies. It’s recommended that the vaccine be given in a medical setting and be supervised by a healthcare provider who is able to recognize and manage serious allergic conditions.

Read more:

The Flu Vaccine Isn't Perfect, But It May Prevent Cases Of Flu-Associated Pneumonia

Do I Need A Flu Shot? CDC Updates Policy On Vaccine Recommendations For 2016 Season