Like all medicines, 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.
Common side effects
The common side effects after all the COVID-19 vaccines happen less often in people aged 65 and older.
You are more likely to experience common side effects after the second dose.
The official name for Moderna's COVID-19 vaccine is 'Spikevax.' But most people call it 'Moderna'.
After the Moderna COVID-19 vaccine, more than 1 in 10 people may experience:
- feeling tired
- tenderness, swelling, redness or itching in your arm where you had the vaccine injection
- swollen lymph glands under the arm where you had the injection
- muscle pain
- joint pain
- nausea or vomiting
- fever (temperature of 38 degrees Celsius or above)
Rare side effects
After the Moderna COVID-19 vaccine more than 1 in 10,000 people may develop:
- Bell's palsy
- swelling of their face - this can happen in people who have had facial fillers
Very rare side effects
Very rarely, people may develop myocarditis and pericarditis after getting the Moderna vaccine. Myocarditis and pericarditis are inflammatory heart conditions.
They mostly happen within 14 days of getting the vaccine and are more likely to occur after the second dose.
Myocarditis is inflammation of the heart muscle. It was reported in around 1 in 1 million doses of the Moderna vaccine.
But the data we have so far shows that the risk of myocarditis is higher for boys and young men.
Based on data from the United States, the estimated risk is:
- 1 in 16,000 in boys aged 12 to 17
- 1 in 20,000 in young men aged 18 to 24
- 1 in 100,000 in girls aged 12 to 17
Pericarditis is inflammation of the outer lining of the heart. It was reported in around 1 in 1 million doses of the Moderna vaccine.
The chance of developing these conditions is very low. But you should know the symptoms so that you can get urgent medical help if you need to.
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:
- palpitations (a forceful heartbeat that may be irregular)
- chest pain
Serious side effects
Serious side effects, like a severe allergic reaction, are extremely rare.
Your vaccinator is trained to treat any serious allergic reactions.
You should not get another mRNA vaccine if you have had a severe allergic reaction to the Moderna vaccine, any of its ingredients or have been told by your doctor not to have the Moderna vaccine.
mRNA vaccines offered in Ireland are the Pfizer/BioNTech vaccine and the Moderna vaccine.
Fever after COVID-19 vaccines
It’s common to develop a fever (temperature of 38 degrees Celsius or above) after any vaccination. This usually happens within 2 days (48 hours) of getting the vaccine. It usually goes away within 2 days.
You are more likely to get a fever after the second dose of your vaccine.
If you feel uncomfortable, take paracetamol or ibuprofen following the instructions on the box or leaflet.
If your fever starts more than 2 days after you are vaccinated, or lasts longer than 2 days, you should self-isolate (stay in your room). Phone your GP to arrange a COVID-19 test.
Updates on COVID-19 vaccine side effects
The COVID-19 vaccines have gone through the same clinical trials and safety checks as all other licensed vaccines. But these vaccines are new and long-term side effect information is limited.
As more people in Ireland and around the world get vaccinated, more information on side effects may become available.
We will update this page with any new information.
If you develop COVID-19 symptoms after your vaccine
COVID-19 vaccines cannot give you COVID-19.
It is possible to have caught COVID-19 before getting your vaccine and not realise you have the symptoms until after your vaccination.
If you have symptoms after the first dose of your COVID-19 vaccine, you still need to have the second dose. While you may get some protection from the first dose, having the second dose will give you the best protection against the virus.
Self-isolate and phone a GP to arrange a COVID-19 test if you have a fever which:
- starts more than 2 days after you get your vaccine
- lasts longer than 2 days after you get your vaccine
Reporting side effects of COVID-19 vaccines
As with all vaccines, you can report suspected side effects to the Health Products Regulatory Authority (HPRA).
There are 2 ways you can report a suspected adverse reaction to a COVID-19 vaccine:
- through the HPRA's online adverse reaction report form
- by emailing or posting this adverse reaction report form to the HPRA (DOCX, 3 pages, 115KB)
As much information as is known should be provided, and where possible, the vaccine batch number should be included. 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.
This content was fact checked by vaccine experts working in Ireland.
Last updated: 11 August 2021 at 4.30pm