Understanding Common Flu Vaccine Side Effects

medica-seed-editor · October 25, 2026, 4:11am

Learn about the most common flu vaccine side effects and how to manage them, as well as the difference between normal reactions and signs that require medical consultation.

What are normal flu vaccine side effects?

Some side effects may appear after receiving the vaccine, whether via intramuscular injection or nasal spray. These are usually an indication that the immune system is reacting and building antibodies. These symptoms include:

Local reactions: Pain, swelling, redness, or stiffness at the injection site in the arm.
General physical reactions: Headache, fatigue, nausea, sweating, or muscle and joint pain.
Fever: A slight increase in temperature may occur, provided it does not exceed 38°C.
Other symptoms: Dizziness or fainting (often related to the injection process itself), and in rare cases, a short period of coughing or mild sore throat.

How to relieve symptoms after vaccination

Most side effects resolve on their own within a day or two. Comfort can be improved by:

Regularly moving the arm that received the injection.
Drinking sufficient fluids.
Avoiding heavy clothing when a fever is present.
Using pain relievers such as ibuprofen or acetaminophen; pregnant women should consult a doctor before taking ibuprofen.

Flu shot side effects requiring medical attention

Immediate medical care should be sought if signs of a severe allergic reaction or abnormal symptoms appear, including:

Difficulty breathing, or the appearance of wheezing or hoarseness in the voice.
Swelling of the lips or the area around the eyes.
Pale skin, rapid heartbeat, or severe dizziness.
Persistent bodily weakness or unusual chills.

Flu vaccine: what to know

Annual influenza vaccination is recommended for everyone aged 6 months and older. It is especially essential for those most prone to complications, such as the elderly, infants, pregnant women, and people with chronic diseases like diabetes and asthma.

Available types of vaccines:

Intramuscular injections: Contain a dead virus and are safe for most people with egg allergies.
Egg-free vaccines: Designed for those with severe egg allergies.
High-dose Fluzone: Given to those aged 65 and older to enhance the immune response.
Nasal spray: Contains a live virus and is used for healthy, non-pregnant individuals aged 2 to 49 years.

Contraindications and alerts:

The vaccine is prohibited for those with a hypersensitivity to its components. Additionally, inform your doctor before vaccination in the following cases:

Diagnosis of Guillain-Barré syndrome.
Receiving a COVID-19 vaccine within the last 14 days.
Having a fever exceeding 38.5°C.
Having received a flu shot less than 6 months ago.

FAQ

When is the best time of year to get the vaccine?

It is preferable to get the vaccine before the start of the flu season, as the body needs approximately two weeks after vaccination to develop antibodies and provide protection.

Can the vaccine cause the flu?

The inactivated vaccine does not contain a live virus; therefore, it cannot cause the flu.

Is vaccinating a pregnant woman beneficial for the fetus?

Yes, vaccinating the mother helps reduce the risk of infection in infants after birth. One study showed a 41% reduction in the risk of infection for infants and a 39% reduction in cases requiring hospitalization.

Medical Disclaimer: This content is for informational purposes only and does not substitute for professional medical advice.