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.

Booster doses

Many countries have given multiple doses of COVID-19 vaccines. There have not been any unexpected side effects for people who have had multiple boosters.

Adapted mRNA vaccines

We expect that the side effects of the adapted (bivalent) mRNA vaccines will be similar to the previous Pfizer/BioNTech and Moderna COVID-19 vaccines.

The safety of the vaccines will continue to be monitored by the European Medicines Agency (EMA).

If you have had anaphylaxis (severe allergic reaction) to Trometamol, you should not get the adapted mRNA vaccines.

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

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

  • 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

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
  • swelling of the lymph glands - more often seen after a booster dose
  • 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)

We do not know the risk of myocarditis or other rare side effects after a booster dose yet.

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 the Pfizer/BioNTech COVID-19 vaccine

Most people can safely get the Pfizer/BioNTech COVID-19 vaccine.

But 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 - they are both mRNA vaccines
  • 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

Moderna COVID-19 vaccine side effects

The Moderna COVID-19 vaccine is called Spikevax.

Moderna - very common side effects

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

These include:

  • feeling tired
  • tenderness or swelling where you had the vaccine
  • headache
  • swollen lymph glands under the arm where you had the vaccine
  • muscle pain
  • joint pain
  • nausea or vomiting
  • fever (temperature of 38 degrees Celsius or above)
  • chills
Moderna - common side effects

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

These include:

  • diarrhoea
  • rash
  • rash, redness, or hives where you had the injection
  • reaction a few days after where you had the injection
Moderna - uncommon side effects

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

These include:

  • itchiness where you had the vaccine injection
  • dizziness
Moderna - rare side effects

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

These include:

  • Bell's Palsy - a weakness in the muscles on one side of your face (that may cause it to droop temporarily)
  • swelling of your face - this can happen in people who have had facial fillers
  • reduced sense of touch or sensation in a part of the body
Moderna - 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.

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

These conditions are more likely to occur after the second dose and mostly happen within 14 days of getting the vaccine.

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

  • 1 additional case for every 7,600 men aged 12 to 29 (within 7 days)
  • 1 additional case for every 5,320 men aged 16 to 24 (within 28 days)

First and second booster doses of mRNA vaccines have not shown any unexpected short-term safety concerns. The risk appears to be comparatively lower following a first booster dose. Data on second booster doses is more limited, but preliminary experience from Israel has not shown any new safety concerns.

Symptoms of myocarditis and pericarditis

Get urgent medical help if you get any of these symptoms in the weeks after the Moderna COVID-19 vaccine:

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

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:

  • 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
  • hypersensitivity reactions (unwanted increased response from the immune system)
  • severe allergic reaction (anaphylaxis)
  • flare-ups of capillary leak syndrome
  • extensive swelling of the vaccinated limb

Symptoms of capillary leak syndrome

Capillary leak syndrome causes fluid to leak from small blood vessels. There is a possible risk of flare-ups in people with a history of capillary leak syndrome. Even though the risk of the condition is extremely low, you should know the signs to watch for.

Get urgent medical help if you get any of these symptoms after the Moderna vaccine:

  • rapid swelling of the limbs (arms and legs)
  • sudden weight gain

You may also feel faint due to low blood pressure.

People usually reported capillary leak syndrome within the first few days of getting this vaccine. Watch out for these symptoms in the days after your vaccination.

Who should not get the Moderna COVID-19 vaccine

The Moderna COVID-19 vaccine is only used in adults aged 30 and over in Ireland.

If you are under 30 and had the Moderna vaccine, you should get the Pfizer/BioNTech vaccine for any other doses you need.

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

  • any of the ingredients in this vaccine - including polyethylene glycol or PEG
  • Trometamol - an ingredient in contrast dyes used for MRI scans

You should also not get this vaccine if you:

  • have been told by a doctor that you should not get this vaccine or the Pfizer/BioNTech COVID-19 vaccine - they are both mRNA vaccines

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
  • have a history of capillary leak syndrome
  • had myocarditis or pericarditis (inflammation of the heart muscle) after a previous dose of any COVID-19 vaccine

Ingredients of Moderna COVID-19 vaccine

The Moderna 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.

Spikevax (Moderna) 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)
  • chills
  • 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:

  • 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 - 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

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 the Novavax COVID-19 vaccine

Most people aged 12 or older can safely get the Novavax COVID-19 vaccine Nuvaxovid.

But 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

Vidprevtyn Beta COVID-19 vaccine side effects

The Vidprevtyn Beta COVID-19 vaccine is available as a booster dose to people age 18 and older.

Vidprevtyn Beta - very common side effects

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

These include:

  • pain where you had the injection
  • headache
  • muscle pain
  • joint pain
  • feeling generally unwell
  • chills
Vidprevtyn Beta - common side effects

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

These include:

  • redness or swelling where you had the injection
  • fever (temperature of 38 degrees Celsius or above)
  • feeling tired
  • nausea
  • diarrhoea
Vidprevtyn Beta - uncommon side effects

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

These include:

  • itchiness where you had the injection
  • bruising where you had the injection
  • warmth where you had the injection
  • swollen lymph glands
Who should not get the Vidprevtyn Beta COVID-19 vaccine

You should not get the Vidprevtyn Beta COVID-19 vaccine if you have had a severe allergic reaction (anaphylaxis) to:

  • a previous dose of this vaccine
  • any of the ingredients in the vaccine (including polysorbate 20 or octylphenol ethoxylate)

Read more about the vaccine ingredients on the European Medicine Agency's website.

Vidprevtyn Beta COVID-19 vaccine - ema.europa.eu

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

  • had a severe allergic reaction (anaphylaxis) in the past, including to any other vaccine or medication

Janssen COVID-19 vaccine side effects

The Janssen COVID-19 vaccine is called Jcovden. It is not currently available in Ireland.

Find a list of side effects of the Janssen vaccine Jcovden on the European Medicines Agency website - ema.europa.eu

AstraZeneca COVID-19 vaccine side effects

The AstraZeneca COVID-19 vaccine is called Vaxzevria. This vaccine is not currently available in Ireland.

Find a list of side effects of the AstraZeneca vaccine Vaxzevria on the European Medicines Agency website - ema.europa.eu

Reporting side effects of COVID-19 vaccines

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.

Most people can have any of the COVID-19 vaccines, but some people are only offered certain vaccines. For example, the Moderna vaccine is only used in adults aged 30 and older.

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

Mpox vaccine

If you recently had the Mpox vaccine, wait 4 weeks before you get vaccinated with a Pfizer, Moderna or Novavax 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: 30 May 2023