Vaccination menu links

Flu vaccine side effects

Flu vaccines are very safe.

If you are concerned about your health at any time please seek advice from your GP or NHS 111.

All medicines can have side effects. The side effects that can happen after a flu vaccine are usually very mild and only last for a day or so.

The most common side effects from a flu injection are a sore arm, mild fever or slight muscle aches.

If you have a sore arm after your vaccination, try these tips to ease it:

  • continue to move your arm regularly
  • use a heat pack or warm compress on the area
  • use an ice pack on the area if it becomes hot and sore – do not apply ice directly to your skin: wrap it in a towel first
  • take a painkiller, such as paracetamol or ibuprofen – follow the directions in the packaging (do not give aspirin to children under 16)

After the nasal spray flu vaccine some children may get a temperature, feel tired, have a headache, aching muscles or reduced appetite for a day or two after having a flu vaccine. The nasal spray may also cause a runny or blocked nose.

The flu vaccine will not cause flu.

If you have what you think is flu after vaccination, it may be that you have caught a flu-like illness that isn't really flu, or you may have caught flu before your flu vaccination had taken effect. Protection usually starts 10-14 days after the flu vaccination.

Any fever after vaccination should be monitored and if you are concerned about your health at any time please seek advice from your GP or NHS 111.

Contact your GP surgery or community pharmacist if you experience any side effects that are not improving over time.

Rare side effects of flu injections

As with all vaccines, there’s a very small chance of a severe allergic reaction (known medically as anaphylaxis).  

Anaphylaxis is very serious, but it can be treated with adrenaline. When it happens, it usually does so within a few minutes of the vaccination. Staff who give vaccinations have all been trained to spot and deal with anaphylactic reactions and children recover completely with treatment.

How to report a suspected vaccine side effect

The Yellow Card Scheme is a national reporting system, which allows you to report suspected side effects from a vaccine. It's run by the Medicines and Healthcare products Regulatory Agency (MHRA), the regulator of medicines and vaccines in the UK.

If you or your child get any side effects from a vaccine, talk to your doctor, pharmacist or nurse. You can also report side effects directly via the MHRA Yellow Card Scheme or search for MHRA Yellow Card in the Google Play or Apple App Store.

Reporting suspected side effects is important. It allows continued monitoring of a vaccine's safety.

For more information visit



Last Updated: 17/02/2022 16:03:02
The information on this page has been adapted by NHS Wales from original content supplied by NHS UK NHS website