Flu vaccine side effects

Flu vaccines are very safe.

A mild fever following a flu vaccine is a common and expected reaction, isolation and COVID-19 testing is not usually required unless COVID-19 is suspected. 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 Direct Wales on 0845 46 47 or NHS 111 Wales if available in your area.

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. (One of the flu vaccines for best protection in older people (aTIV) is more likely to cause a sore arm)

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 – 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 .

Allergic reactions to a flu vaccine

Serious allergic reactions (such as anaphylaxis) to flu vaccines are very rare. Healthcare staff giving vaccinations are fully trained to deal with this, and with prompt treatment, individuals make a quick and complete recovery.

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

How to report a suspected vaccine side effect

The Yellow Card Scheme allows you to report suspected side effects from a vaccine. It's run by a medicines safety watchdog called the Medicines and Healthcare products Regulatory Agency (MHRA) and it's a good way to of monitoring a vaccine's safety.


Click here to see all vaccination leaflets.

Last Updated: 11/11/2019 13:11:33
The information on this page has been adapted by NHS Wales from original content supplied by NHS UK NHS website