The Real Reason You Might Get A Fever After The Flu Shot

Getting your yearly flu shot is a safe and effective way to help protect yourself and others from contracting the flu — but can it actually make you sick? Like with any vaccine, the flu shot comes with a set of potential side effects. While these mild and temporary side effects may be unpleasant or uncomfortable, they're actually a sign that the vaccine is working (via CNET).

That's because the flu vaccine works by introducing an inactivated version of the flu virus into your body, which generates an immune response that can sometimes lead to flu-like side effects. "The flu vaccine is designed to stimulate your immune system to build antibodies to the virus," Dr. Carmen Teague, specialty medical director at Atrium Health's Mecklenburg Medical Group, told CNET. "That stimulation can cause a low-grade fever, a decrease in appetite, loose stool, mild fatigue or myalgia (muscle ache), and even a scant cough."

While most people don't experience any side effects after receiving the flu vaccine, symptoms that do occur should only last for a handful of days (via Healthline). For instance, it's not unusual to experience a low-grade fever shortly after getting the flu shot. A low-grade or slight fever is defined as a fever below 101 degrees Fahrenheit. However, it should dissipate within a day or two, and can easily be treated with over-the-counter medicine, like ibuprofen or acetaminophen.

If your fever gets worse or persists for more than 2 days, however, it might be the result of another illness. In fact, you may have caught a cold or contracted another common virus, known as respiratory syncytial virus (RSV). Both can cause a number of flu-like symptoms (via Prevention). It's also within the realm of possibility that you may contracted the flu shortly before getting the vaccine.