Understanding the Side Effects of Each COVID-19 Vaccine: What You Need to Know

As the UK continues to manage COVID-19 as an endemic virus, vaccination remains one of the most effective ways to prevent severe illness and hospitalisation. 

However, it’s perfectly natural to want to understand what side effects might occur after getting your jab or booster

Here’s a straightforward guide to the most common, less common and rare side effects for each of the main vaccines used in the UK: Pfizer-BioNTech (Comirnaty), Moderna (Spikevax), Novavax, and the earlier AstraZeneca vaccine.

Pfizer-BioNTech (Comirnaty)

Pfizer is the most widely used COVID-19 vaccine in the UK and has an excellent safety record.

Common side effects:

Soreness or redness where the injection was given

Fatigue and mild headache

Muscle or joint pain

Slight fever or chills

Feeling generally under the weather for a day or two

Less common effects:

Swollen lymph nodes (especially under the arm where you were jabbed)

Nausea or mild dizziness

Rare effects:

Myocarditis or pericarditis (inflammation of the heart or its lining), particularly in young men. Symptoms include chest pain, shortness of breath, or a fluttering heartbeat. This reaction is rare and usually mild.

Moderna (Spikevax)

Moderna works in a similar way to Pfizer and offers strong protection.

Common side effects:

Pain, swelling, or redness at the injection site

Headache and tiredness

Mild fever or chills

Muscle or joint aches

Less common effects:

Swelling of the lymph nodes

Temporary skin rash or itching

Menstrual cycle changes, though these are short-term

Rare effects:

Myocarditis and pericarditis, again mainly seen in younger men after the second dose. These cases are rare and usually resolve with rest and medical care.

Novavax

Novavax, a protein-based vaccine, is sometimes offered as an alternative for those who cannot have an mRNA vaccine.

Common side effects:

Tenderness at the injection site

Headache, fatigue, or feeling feverish

Muscle pain or nausea

Less common effects:

Mild swelling of lymph nodes

Dizziness or slight changes in blood pressure

Rare effects:

Allergic reactions (very uncommon and treated immediately if they occur)

AstraZeneca (Vaxzevria)

While no longer routinely used for boosters in the UK, many people received AstraZeneca for their primary doses.

Common side effects:

Soreness or mild swelling at the injection site

Fatigue and headache

Mild fever, chills, or flu-like symptoms lasting 24–48 hours

Less common effects:

Nausea or mild vomiting

Feeling faint or light-headed

Rare effects:

Blood clots with low platelets (thrombosis with thrombocytopenia syndrome) – a very rare side effect, affecting fewer than 15 people per million doses

Severe allergic reactions (extremely rare and treated promptly)

What You Should Do After Vaccination

If you experience mild side effects such as soreness, headache or fever, these can usually be managed with rest and paracetamol. They are signs that your immune system is responding as it should.

However, seek urgent medical advice from NHS 111 or your GP if you develop:

Chest pain or persistent pressure

Shortness of breath

Swelling, blurred vision or severe headache

Unusual bruising or bleeding

A rash that doesn’t fade when pressed

COVID-19 vaccines continue to undergo thorough safety monitoring by the Medicines and Healthcare products Regulatory Agency (MHRA). 

Millions of doses have been safely administered across the UK, and the benefits of vaccination far outweigh the small risk of side effects.

For personalised medical advice, especially if you have a history of allergic reactions or heart conditions, speak to your GP or local vaccination centre before booking your next dose.

Stay informed. Stay healthy. Stay protected.

For more updates on vaccination, health and wellbeing, visit That’s Health.