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Flu and COVID-19: What to expect after, adults


Flu and COVID-19 vaccinations

What to expect after flu and COVID-19 vaccinations for adults

August 2022


This leaflet tells you what to expect after your flu and COVID-19 vaccines.

All the flu and COVID-19 vaccines given by NHS Wales have been authorised for use across the UK by the Medicines and Healthcare products Regulatory Agency (MHRA). The MHRA continues to review the safety of vaccines based on reporting by healthcare professionals and the public.


Will I get any side effects?

Like all medicines, vaccines can cause side effects. This is because vaccines work by prompting a response in your immune system. Most side effects are mild and short-term, and not everyone gets them.

Very common side effects in the first day or two include:

  • a heavy feeling or soreness where you had the injection
  • general aches or flu-like symptoms
  • feeling tired
  • having a headache, and
  • a mild fever.

If your arm is particularly sore, you may find heavy lifting difficult.

If you feel unwell or very tired, you should rest and avoid operating machinery or driving.

You may have a mild fever for two or three days after your 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.

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 about 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.

There have been reports of an extremely rare condition involving blood clots and unusual bleeding after vaccination with the AstraZeneca vaccine. This is being carefully monitored, but the risk factors for this condition are not yet clear.

The Joint Committee on Vaccination and Immunisation (JCVI) advises there is a much lower rate of blood clots and unusual bleeding with second and booster doses. Because of the high risk of complications and death from COVID-19, the Medicines and Healthcare products Regulatory Agency (MHRA), the World Health Organization (WHO) and the European Medicines Agency (EMA) have concluded that the balance is very much in favour of vaccination for the vast majority of adults.

If you experience any of the following from around four days to four weeks after your vaccination, you should get medical advice urgently.

  • A new, severe headache which is not helped by usual painkillers or is getting worse.
  • An unusual headache which seems to get worse when lying down or bending over or may be accompanied by:
    • blurred vision, nausea and vomiting
    • difficulty with your speech, or
    • weakness, drowsiness or seizures.
  • New, unexplained pinprick bruising or bleeding.
  • Shortness of breath, chest pain, swelling in the legs or persistent abdominal pain.

Rare cases of inflammation of the heart (called myocarditis or pericarditis) have been reported after some COVID-19 vaccinations. 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 vaccine you have had so they can assess you fully.


Reporting side effects

You can also report suspected side effects of vaccines and medicines through the Yellow Card scheme. You can do this online by searching Yellow Card scheme, by downloading the Yellow Card app, or by calling 0800 731 6789 (Monday to Friday, 9am to 5pm).


Will the vaccines protect me?

Having a yearly flu vaccine is one of the best ways to protect against catching and spreading flu. Having a COVID-19 vaccine reduces the chance of you suffering from severe illness or dying from COVID-19.

Protection from both vaccines generally starts a few weeks after having them. Like all medicines, no vaccine is completely effective. You might still get flu or COVID-19, but your symptoms are likely to be milder.


More information

You can find more information on vaccines offered in Wales at:

You can find out more information about vaccines, including their contents and possible side effects, at: You will need to enter the name of the vaccine in the search box.

If you have any questions or want more information, you can visit:, talk to your doctor or nurse or call NHS 111 Wales.

You can report suspected side effects online at or by downloading the Yellow Card app, or calling 0800 731 6789 (Monday to Friday, 9am to 5pm).

To find out how the NHS uses your information, visit:

For other formats of this leaflet, visit:


© Public Health Wales, August 2022

(with acknowledgement to UK Health and Security Agency)

Version 1