What Are the Most Common Side Effects of a Flu Shot?

A fellow caregiver asked...

What are the most common side effects of a flu shot?

Expert Answer

Dr. Leslie Kernisan is the author of a popular blog and podcast at BetterHealthWhileAging.net. She is also a clinical instructor in the University of California, San Francisco, Division of Geriatrics.

The possible side effects depend on which type of vaccination you get. There are two ways to be vaccinated against the seasonal flu: You can get the intramuscular injection (commonly called the flu shot) of inactivated influenza, which contains killed virus. Or you can get the nasal spray vaccine (also known as FluMist), which contains live but weakened influenza vaccine.

The flu shot can cause a sore arm, and it sometimes causes mild fever, achiness, and fatigue that can feel like a mild case of flu to some people. But those symptoms generally don't last for more than a day or two. The nasal vaccine has been linked to symptoms such as runny nose, cough, and sore throat.

Both vaccine types contain traces of chicken eggs, which can be a problem for those with egg allergies.

You should know that only the inactivated influenza vaccine (the shot) is recommended for adults older than 50, or for those with known weakened immune systems (such as those with HIV).

Keep in mind that even though it's not uncommon to notice some mild side effects in the days after you get a flu vaccine, the risks associated with not getting vaccinated -- and getting the flu -- are quite serious. On average, every year 36,000 Americans die from seasonal influenza.

If you're younger than 50, talk to your doctor to help you decide which form of vaccination makes the most sense for you.