Like all medicines, vaccines can cause side effects. This is because vaccines work by triggering a response in your immune system. Most of these are mild and only last a few days, and not everyone gets them.
A mild fever may occur for two to three days after vaccination but a high temperature is unusual and may indicate you have COVID-19 or another infection. You can take paracetamol (follow the advice on dose and intervals in the packaging) and rest to help you feel better. Do not take more than the recommended dose.
An uncommon side effect 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 see your doctor. If you are due for breast screening (a mammogram) in the few weeks after the vaccine, then you should mention you’ve had the COVID-19 vaccine when you attend.
Common side effects following vaccination normally last less than a week. If your symptoms seem to get worse or you are concerned, look at: https://111.wales.nhs.uk/ online, and if necessary call NHS 111 Wales on 111 or your GP surgery. If 111 is not available in your area, call 0845 46 47. Calls to NHS 111 Wales are free from landlines and mobiles. Calls to 0845 46 47 cost 2p per minute plus your telephone provider’s usual access charge.