You’ve rolled up your sleeve, gotten your flu shot and are feeling good about protecting yourself from a season of sniffles and fevers. And then it hits you. The achy, swollen arm. The “did I just run a marathon?” fatigue.
Flu shots are one of the best defenses against serious illness. Like most vaccines, they can come with a few mild, and short-lived, side effects. Here’s what you might notice after your flu shot, simple things you can do to feel better at home and when it’s time to check in with your doctor.
Common Flu Shot Symptoms
After your flu shot, you may experience some minor side effects. These are normal signs that your immune system is building protection. Most flu shot side effects are mild and short-lived. Here’s what you might notice after your flu shot:
- Arm pain or swelling at the injection site
- Fatigue
- Headache
- Low-grade fever, especially in children
“Mild side effects are a normal part of the vaccine process,” says Brian Curtis, MD, vice president, chief medical officer for OSF Medical Group. “They indicate your body is making antibodies that will protect you later, without you having to experience the illness itself.”
Less Common Flu Shot Side Effects
Some reactions are less frequent but still normal as your body responds to the vaccine. Most go away on their own within a few days. Less common side effects after the flu shot include:
- Rash or itching near the injection site
- Mild neck pain
- Back pain
Rare Flu Shot Side Effects
In rare cases, flu shots can cause more serious symptoms that require immediate attention. These rare side effects after a flu shot include chest pain, heavy or ongoing bleeding and hives, swelling or trouble breathing. Some of these side effects may indicate you are having an allergic reaction.
Unsure if your side effects are normal?
If you experience any of these symptoms, call 9-1-1 or go to the nearest emergency department.
“Serious reactions are extremely rare,” says Dr. Curtis. “For most people, the risk of complications from the flu itself far outweighs the minimal chance of a severe vaccine response.”
Can the flu shot make you sick?
While the flu shot does typically come with mild side effects, it cannot give you the flu or make you sick.
“It’s a common myth that the flu shot can give you the flu,” says Dr. Curtis. “In reality, the vaccine contains either inactivated virus or pieces of the virus that cannot cause infection.”
Can the flu shot give you diarrhea?
Diarrhea is uncommon after a flu shot and is usually caused by something else, like a stomach virus. If these symptoms last for more than 2-3 days, it’s a good idea to call your primary care provider.
How to Relieve Flu Shot Side Effects at Home
The good news is most flu shot side effects usually only last one to three days. While you wait for them to go away, there are some steps you can take.
If your arm is feeling sore, try applying a cold pack for 10–15 minutes at a time to reduce soreness and swelling. Make sure to keep moving your arm gently to prevent stiffness, but avoid heavy lifting or intense workouts until the soreness fades. Over-the-counter pain relievers like acetaminophen or ibuprofen can help with pain, fever or body aches.
“Staying hydrated and getting extra rest after your flu shot can also help,” says Dr. Curtis. “Think of it as giving your body the fuel and downtime it needs to support your immune system as it builds protection.”
When to Call Your Doctor
Reach out to your primary care provider if your flu shot side effects last longer than two to three days or if you develop a high fever or severe pain. For urgent situations, like chest pain, trouble breathing or signs of a severe allergic reaction, seek emergency care right away.
Last Updated: October 20, 2025