COVID-19 vaccines and cardiac inflammation

Cases of myocarditis and pericarditis after COVID-19 vaccines are rare: mostly reported in males under 40 years of age, after the second dose. Cases do occur in both females and males, at any age, and after any dose, including a third or fourth dose. Most cases are mild and patients recover quickly.

Myocarditis and pericarditis

There is a link between COVID-19 vaccines and rare side effects of myocarditis and pericarditis.

  • Myocarditis is inflammation of the heart muscle.
  • Pericarditis is inflammation of the pericardium (the thin, sac-like tissue surrounding the heart muscle).

Myocarditis and pericarditis can occur together or separately. 

Myocarditis and pericarditis occur in the general population from a variety of causes. Not all cases that occur after vaccination are caused by the vaccine. Myocarditis and pericarditis can also be caused by COVID-19.

Myocarditis and pericarditis have been reported most frequently in males under 40 years of age and after the second vaccine dose. However, myocarditis or pericarditis can happen in any gender and after any dose. Up-to-date information on cases and rates reported to the Therapeutic Goods Administration (TGA) is available at: www.tga.gov.au/periodic/covid-19-vaccine-weekly-safety-report.

The risk of myocarditis is higher (although still rare) after Moderna vaccination compared with Pfizer. It is estimated there are around 2 more cases per 100,000 second vaccine doses in Moderna recipients (younger than 40 years) than Pfizer recipients (younger than 40 years).

New evidence suggests that Vaxzevria (AstraZeneca) and Nuvaxovid (Novavax) are probably associated with a small increased risk of myocarditis and pericarditis.

This risk after AstraZeneca looks lower than the risk after Moderna or Pfizer. The small number of total doses of Novavax COVID-19 vaccine given globally prevents the calculation of a precise risk at this time.

ATAGI will continue to monitor data as it emerges and update advice accordingly.

There is no evidence to suggest myocarditis or percarditis is more severe following either vaccine.

Most myocarditis and pericarditis cases linked to COVID-19 vaccination have been mild and patients have recovered quickly. Longer-term follow-up of these cases is ongoing.

The risk of myocarditis and pericarditis looks much lower in children aged 5 to 11 years compared to adolescents. The risk also looks lower after a booster than the primary course.

In children aged 6 months to less than 5 years, there is no clear attributable risk of myocarditis and pericarditis after COVID-19 vaccines.

A longer interval between doses of the primary course may reduce the likelihood of myocarditis and pericarditis by a small amount. A longer interval may also improve vaccine protection. The recommended interval between 2 doses of Pfizer, Moderna, or Novavax vaccine is 8 weeks. The interval can be shortened in some circumstances (such as for people with increased risk of severe COVID-19) to 3 weeks for Pfizer and Novavax or 4 weeks for Moderna and AstraZeneca.

Guidance

The Australian Technical Advisory Group on Immunisation (ATAGI) and the Cardiac Society of Australia and New Zealand (CSANZ) have jointly developed guidance on managing these conditions. 

The guidance contains advice on assessment, management and follow up. 

Risk/benefit profile

ATAGI emphasise that the overwhelming benefits of vaccination in protecting against COVID-19 greatly outweigh the rare risk of these conditions.

People aged 6 months and over can be vaccinated against COVID-19 if they do not have any contraindications to the vaccine.

During the consent process, advise people receiving mRNA vaccines:

  • there is a rare risk of myocarditis or pericarditis
  • what symptoms to look out for. 

Pre-existing cardiac conditions

Most pre-existing cardiac conditions are not contraindications to vaccination. Some patients should consult a GP or cardiologist about the best timing for vaccination and if any additional precautions are needed.

See the guidance document for details. 

Symptoms

Symptoms of myocarditis or pericarditis typically appear within 1 to 5 days of vaccination. People who experience any of these symptoms after having an mRNA COVID-19 vaccine should seek prompt medical attention:

  • chest pain
  • pressure or discomfort in the chest
  • irregular, skipped heartbeats or ‘fluttering’
  • fainting
  • shortness of breath
  • pain when breathing.

Initial investigations for people presenting with symptoms or signs of myocarditis or pericarditis should include ECG, troponin, chest X-ray, and other investigations for other differential diagnoses as clinically indicated.

People who develop myocarditis or pericarditis attributed to their first dose of mRNA vaccine should defer further doses and discuss this with their treating doctor.

Referral to cardiologist

People who experience myocarditis and/or pericarditis after an mRNA COVID-19 vaccine should be referred to a cardiologist for further assessment and management, to investigate for possible causes other than vaccination, and for follow-up.

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