Like all medicines, vaccines can cause side effects. Most side effects are mild and short-term, and not everyone gets them.
The most common side effects should only last a day or two, and include:
a heavy feeling or soreness where you had the injection
general aches or mild flu-like symptoms
feeling sick or vomiting
diarrhoea
tiredness
headache, and
mild fever.
Babies under two years old may also be irritable, sleepy and lose their appetite.
You may have a mild fever for two to three days after having a vaccine. However, a high temperature is unusual and may be because you have another infection or illness. If you are worried, speak to your doctor or nurse.
You can take paracetamol (follow the advice in the packet and do not take more than the recommended dose), and rest to help you feel better. Children under 16 should not be given medicines that contain aspirin.
An uncommon side effect after the COVID-19 vaccine is swollen glands in the armpit or neck, on the same side as the arm where you had the vaccine. This can last for around 10 days, but if it lasts longer contact your GP surgery for advice. If you are due for breast screening (a mammogram) in the few weeks after the vaccine, mention you’ve had the COVID-19 vaccine when you attend.
Very rarely cases of inflammation of the heart have been reported after some COVID-19 vaccines. This is called myocarditis or pericarditis. These cases have been seen mostly in younger men within several days after vaccination. Most of these people recovered and felt better following rest and simple treatment.
You should get medical advice urgently if you have:
chest pain
shortness of breath, or
a fast-beating, fluttering, or pounding heart.
Other side effects are uncommon or very rare.
If your symptoms seem to get worse or if you are concerned, call NHS 111 or your GP surgery. If you do get advice from a doctor or nurse, make sure you tell them what vaccines you have had so they can assess you fully. You can also go to 111.wales.nhs.uk (external site) online.