Getting the influenza (flu) vaccine each year is one of the most effective ways to protect yourself and others from seasonal influenza and its complications. While the vaccine is safe and well-tolerated by most people, some may experience mild, short-lived symptoms afterward—often described as “flu-like symptoms.” These side effects can raise questions or cause concern, particularly for those receiving the vaccine for the first time.
This guide explains why these symptoms may occur, what’s considered normal, and when it’s important to speak with your GP.
How the Flu Vaccine Works
The flu vaccine helps your immune system recognise and respond to the influenza virus. It contains inactivated (killed) parts of the virus or proteins that mimic it—enough to stimulate a protective immune response but not enough to cause infection.
“In Australia, only inactivated influenza vaccines are used. These vaccines do not contain any live virus. As such, they cannot give you the flu.”
Once vaccinated, it takes approximately two weeks for your body to build full immunity. During this time, you may still be vulnerable to catching the virus if exposed.
Flu-like Symptoms After Flu Shots
Some people report feeling slightly unwell after getting the flu shot. This is generally a normal response, not a sign of illness. These symptoms reflect your immune system’s activation—and its preparation to defend against future flu infections.
Possible causes include:
Immune response – Your body is producing antibodies. This may cause mild fatigue, low-grade fever, or muscle aches for 1–2 days.
Coincidental infection – Cold and respiratory viruses are common during flu season. You may develop symptoms from a separate infection.
Exposure timing – If you’re exposed to the flu virus shortly before or just after your vaccination, you may still get sick before the vaccine becomes effective.
Common Side Effects: What’s Normal?
Most side effects are mild and resolve on their own within 24 to 48 hours.
Local (injection site) symptoms:
Pain or soreness
Redness
Swelling
Warmth at the site
General symptoms:
Fatigue
Mild headache
Low-grade fever (under 38.5°C)
Muscle aches
Mild chills or discomfort
These are all common signs that your body is responding appropriately to the vaccine. They do not indicate that you are infected.
Rare and Serious Reactions: When to See a Doctor
While serious side effects are uncommon, it's important to know when to seek medical attention. Contact your GP or visit your local emergency department if you experience:
High fever (above 39°C) or fever lasting more than 48 hours
Severe headache or confusion
Swelling of the face, lips, tongue, or throat
Difficulty breathing
Hives or widespread rash
Dizziness, fainting, or rapid heartbeat
These may be signs of an allergic reaction or another medical condition requiring urgent evaluation.
Rare conditions to be aware of:
Guillain-Barré Syndrome (GBS) – A very rare condition where the immune system attacks the nerves. This has been reported in about 1–2 cases per million flu vaccines.
Oculo-respiratory syndrome (ORS) – A rare and mild condition causing red eyes, cough, and facial swelling. It usually resolves on its own.
If you are concerned about any symptoms, contact your healthcare provider.
Managing Symptoms at Home
For mild side effects, you can manage symptoms at home with simple measures:
Rest and allow your immune system to do its job.
Hydration is essential—drink plenty of water.
Use paracetamol or ibuprofen if needed for pain or fever (unless contraindicated).
Apply a cool compress to the injection site to reduce swelling.
Symptoms typically improve within 1–2 days. If they persist or worsen, seek medical advice.
Who Should Get the Flu Vaccine?
Annual influenza vaccination is recommended for all Australians aged six months and older, particularly those at higher risk of severe illness.
The National Immunisation Program provides free flu vaccines for:
Children aged 6 months to under 5 years
Adults aged 65 and over
Pregnant women
Aboriginal and Torres Strait Islander people
People with chronic medical conditions
Frontline healthcare and aged care workers
Getting vaccinated helps protect not only yourself but also your family, colleagues, and community.
Frequently Asked Questions
Can the flu vaccine give me the flu?
No. The vaccines used in Australia contain inactivated virus particles and cannot cause influenza.
Why do I feel sick after the shot?
Flu-like symptoms are a normal immune response. They are typically mild and short-lived.
How long do side effects last?
Most symptoms resolve within 24–48 hours.
Can I still get the flu after being vaccinated?
Yes. The vaccine covers the most common strains but not all. Immunity also takes about two weeks to develop.
What if I develop symptoms a week or more after the shot?
It’s unlikely these are due to the vaccine. You may have caught another virus. Consult your GP if symptoms persist.
When in Doubt, Talk to Your GP
At North Brighton Medical Centre, we understand that you may have questions or concerns about the flu vaccine — from possible side effects to how it fits with your individual health needs. Our GPs are here to offer clear, personalised advice based on your medical history.
Flu vaccines save lives. Understanding what to expect after vaccination can help you feel more confident in your decision to protect yourself and others.