Like all medicines, vaccines can cause side effects. Most of these are mild and don’t last long, and not everyone gets them. The most common side effects should only last a day or two.
The most common side effects in the first day or two are:
soreness and redness at the site of the injection
tiredness
feeling sick or vomiting
diarrhoea
headache, and
fever.
Babies under two years old may also be irritable, sleepy and lose their appetite.
You or your child may have a mild fever for two to three days, but a high temperature is unusual and may mean you have another infection or illness. You can take the normal dose of paracetamol (follow the advice in the packet and do not take more than the recommended dose) and rest to help you feel better.
Remember – babies and children under 16 should not take medicines that contain aspirin.
These symptoms normally last less than a week. If your symptoms seem to get worse, or if you are concerned, go to 111.wales.nhs.uk online. If necessary, call NHS 111 Wales by dialling 111, or call your GP surgery. Calls to NHS 111 Wales are free from landlines and mobiles.
Serious side effects
Rare cases of inflammation of the heart (called myocarditis or pericarditis) have been reported after some COVID-19 vaccines. These cases have been seen mostly in younger men within several days after vaccination.
You can find more information about myocarditis or pericarditis in the next question.