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Side effects and safety of COVID-19 vaccines

Like all medicines, COVID-19 vaccines can cause side effects. Most of these are mild to moderate and short-term. Not everyone gets side effects.

If you are concerned about side effects, phone your GP for advice.

Serious side effects, like a severe allergic reaction, are extremely rare. Your vaccinator is trained to treat allergic reactions.

Fever after COVID-19 vaccines

It’s common to develop a fever (temperature of 38 degrees Celsius or above) after COVID-19 vaccination. This usually happens within 48 hours of getting a vaccine.

If you feel uncomfortable, take paracetamol or ibuprofen following the instructions on the box or leaflet.

Side effects of COVID-19 vaccines

The side effects of the COVID-19 vaccines used in Ireland are listed below.

Pfizer/BioNTech COVID-19 vaccine side effects

The Pfizer/BioNTech COVID-19 vaccine is called Comirnaty.

Pfizer/BioNTech - very common side effects

Very common side effects may affect more than 1 in 10 people.

These include:

  • tenderness or swelling in your arm where you had the vaccine
  • feeling tired
  • headache
  • muscle pain
  • joint pain
  • diarrhoea
  • fever (temperature of 38 degrees Celsius or above)
  • chills

For children age 6 months to 23 months, these include:

  • irritability
  • drowsiness
  • redness in the arm where they had the vaccine
  • decreased appetite
Pfizer/BioNTech - common side effects

Common side effects may affect up to 1 in 10 people.

These include:

  • nausea
  • vomiting
  • redness in your arm where you had the vaccine
  • swelling of the lymph glands - more often seen after a booster dose

For children age 6 months to under 2 years, this includes:

  • a rash
Pfizer/BioNTech - uncommon side effects

Uncommon side effects may affect up to 1 in 100 people.

These include:

  • itchiness where the vaccine was given
  • itchiness in general
  • a rash
  • sleeplessness
  • excessive sweating
  • night sweats
  • decreased appetite
  • lethargy, asthenia (lack of energy) and malaise (feeling unwell)
  • pain in the arm where you had the vaccine
  • dizziness
Pfizer/BioNTech - rare side effects

Rare side effects may affect up to 1 in 1,000 people.

These include:

  • an allergic reaction that can cause hives or swelling of the face
  • weakness in the muscles on one side of your face (that may cause it to droop temporarily)
Pfizer/BioNTech - very rare side effects

Very rare side effects may affect up to 1 in 10,000 people.

These include:

  • myocarditis
  • pericarditis

Myocarditis and pericarditis are inflammatory heart conditions. These conditions are more likely to happen after the second dose. They have mostly been seen within 14 days of getting the vaccine.

The risk of these very rare conditions is higher in young men.

2 European studies have estimated the risk of myocarditis in men, after the second dose of the vaccine as:

  • 1 additional case for every 38,000 men aged 12 to 29 (within 7 days)
  • 1 additional case for every 17,500 men aged 16 to 24 (within 28 days)

The risk of myocarditis is lower after a booster dose.

Symptoms of myocarditis and pericarditis

Get urgent medical help if you get any of these symptoms in the weeks after the Pfizer/BioNTech vaccine:

  • breathlessness
  • palpitations (a forceful heartbeat that may be irregular)
  • chest pain

Signs of myocarditis in younger children may be more general including:

  • irritability
  • vomiting
  • difficulty feeding
  • rapid and shallow breathing
  • fatigue
Pfizer/BioNTech - extremely rare side effects

We do not know yet how many people are affected by extremely rare side effects. There is not enough data available at this time.

These include:

  • extensive swelling of the limb where you got your vaccine
  • tingling or prickling sensation, or loss of sensation in some part of the body
  • people who have had facial fillers may develop swelling of their face
  • a severe allergic reaction (anaphylaxis)
  • erythema multiforme - a skin reaction that causes red spots or patches on the skin. It may look like a target or 'bulls-eye' with a dark red centre surrounded by paler red ring
  • heavy menstrual bleeding (periods)

Who should not get this vaccine

Most people can safely get the Pfizer/BioNTech COVID-19 vaccine. You will be offered a different vaccine if this vaccine is not suitable.

Who should not get the Pfizer/BioNTech COVID-19 vaccine

This vaccine is not recommended if you:

  • have had a severe allergic reaction to any of the ingredients in this vaccine - including polyethylene glycol or PEG
  • have been told by a doctor that you should not get this vaccine or the Moderna vaccine
  • have had a severe allergic reaction to a previous dose of this vaccine or the Moderna vaccine
  • have had a severe allergic reaction after Trometamol (one of the contents in contrast dye used in MRI radiological studies)

Talk to your doctor before getting this vaccine if you:

  • have had a severe allergic reaction (anaphylaxis) in the past, including to any other vaccine or medication
  • had myocarditis or pericarditis (inflammation of the heart muscle) after a previous dose of any COVID-19 vaccine

Ingredients of Pfizer/BioNTech COVID-19 vaccine

The Pfizer/BioNTech COVID-19 vaccine does not contain eggs, preservatives or latex.

You can read more about the vaccine ingredients on the European Medicine Agency's website.

Comirnaty (Pfizer/BioNTech) COVID-19 vaccine - ema.europa.eu

Novavax COVID-19 vaccine side effects

The Novavax COVID-19 vaccine is called Nuvaxovid.

Novavax - very common side effects

Very common side effects may affect more than 1 in 10 people.

These include:

  • feeling tired
  • feeling generally unwell
  • headache
  • nausea or vomiting
  • muscle pain
  • joint pain
  • tenderness or pain in your arm where you had the vaccine injection
Novavax - common side effects

Common side effects may affect up to 1 in 10 people.

These include:

  • fever (temperature of 38 degrees Celsius or above)
  • pain in extremities (arm, hand, leg or foot)
  • redness or swelling where the vaccine was given
Novavax - uncommon side effects

Uncommon side effects may affect up to 1 in 100 people.

These include:

  • chills
  • swelling of the lymph glands
  • high blood pressure lasting for a few days after vaccination
  • a rash
  • redness of the skin
  • general itchiness
  • itchiness where the vaccine was given
  • hives

Some side effects are seen more often after the second dose.

Novavax - rare side effects

Rare side effects may affect up to 1 in 1000 people.

These include:

  • feeling warm where you had the injection
Novavax - extremely rare side effects

We do not know yet how many people are affected by extremely rare side effects. There is not enough data available at this time.

Extremely rare side effects include:

  • tingling or prickling sensation
  • loss of sensation in some parts of the body
  • myocarditis and pericarditis
  • a severe allergic reaction (anaphylaxis)

Symptoms of myocarditis and pericarditis 

Myocarditis and pericarditis are inflammatory conditions of the heart. Even though the risk of these conditions is very low, you should know the signs to look for. 

These conditions can develop a few days after vaccination. They have mostly been seen within 14 days.

Get medical help if you get any of these symptoms after you get this vaccine:

  • breathlessness
  • palpitations (a forceful heartbeat that may be irregular)
  • chest pain

Who should not get this vaccine

Most people aged 12 or older can safely get the Novavax COVID-19 vaccine Nuvaxovid. It is usually offered if the Pfizer/BioNTech COVID-19 vaccine is not suitable.

Who should not get the Novavax COVID-19 vaccine

This vaccine is not recommended if you have had a severe allergic reaction to:

  • a previous dose of the vaccine
  • any of the ingredients in the vaccine (including polysorbate 80)

You can read more about the vaccine ingredients on the European Medicine Agency's website.

Talk to your doctor before getting a COVID-19 vaccine if you:

  • have had a severe allergic reaction (anaphylaxis) in the past, including to any other vaccine or medication
  • had myocarditis or pericarditis (inflammation of the heart muscle) after a previous dose of any COVID-19 vaccine

Nuvaxovid COVID-19 vaccine - ema.europa.eu

Vaccines previously offered

Side effects of COVID-19 vaccines previously offered in Ireland.

Find a:

Reporting side effects

As with all vaccines, you can report suspected side effects to the Health Products Regulatory Authority (HPRA).

COVID-19 vaccine adverse reaction report - hpra.ie

If you are reporting a side effect to the HPRA

Give as much information as possible. Include the vaccine batch number if you have it. You'll find this on your vaccine record card. You can also ask your doctor or a family member to report side effects for you.

The HPRA cannot provide clinical advice on individual cases. Talk to your doctor or pharmacist about any medical concerns you may have.

Safety of COVID-19 vaccines

All vaccines are tested to make sure they are safe and work before they can be used. The HSE only uses a vaccine if it meets the required standards of safety and effectiveness.

You will be offered the vaccine that is most suitable for you.

It is expected that the safety of the adapted vaccines will be similar to the previous vaccines. The safety of COVID-19 vaccines will continue to be monitored by the EMA.

Mpox vaccine

If you recently had the Mpox vaccine, wait 4 weeks before you get vaccinated with any COVID-19 vaccine. This is a precaution because of the unknown risk of myocarditis.

This content was fact checked by vaccine experts working in Ireland.

Page last reviewed: 7 December 2023