Myocarditis and pericarditis have been recognised as rare cardiac complications of COVID-19 mRNA vaccinations. Myocarditis is the inflammation of the heart muscle, whereas pericarditis is the inflammation of the outer lining (membrane) of the heart. Globally, this has generally been observed to occur mainly in young adults especially adolescent males <30 years old, within 3 – 5 days of administration of the second dose of the vaccine. Cases have mostly been mild, self-limiting or with good response to treatment; majority of hospitalisations were of short durations in non-ICU settings.
Although the exact mechanism for myocarditis post mRNA vaccination is unknown, one suggested postulation is that of genetic predisposition coupled with a hyperimmune response leading to myocardial injury.
Epidemiology
| Myocarditis/Pericarditis | ||
| Reported rates post- mRNA vaccination | Background rates | |
| US | US Centers for Disease Control and Preventiono (CDC) (Jul 2021): 12.6 cases per million doses of second-dose mRNA vaccine among individuals 12 to 39 years of age | Common viral myocarditis: 1 to 10 cases per 100 ,000 person-years |
| Singapore | Singapore’s Health Sciences Authority (HSA) (Nov 2021): 94 reports of myocarditis and pericarditis following more than 10.63 million doses of mRNA vaccines administered i.e. ~0.96 per 100,000 doses administered. | Incidence of myocarditis/pericarditis leading to hospitalisation in the general population: ~5 to 7 per 100,000 persons per year, or about 280 to 400 cases a year. |
| Israel | The Israeli Ministry of Health also reported 148 myocarditis cases among 10.4 million vaccinated individuals occurring within 30 days of mRNA vaccination, a majority after a second dose, mostly in males 16 to 30 years of age. | A global estimate of incidence is 22 cases per 100 000 person-years. |
Notably, cardiac inflammation may also result from COVID-19 infection. The overall incidence of COVID-19 mRNA-vaccine-related myocarditis seems to be low, estimated as 0.3–5.0 cases per 100,000 vaccinated people in case-series studies from the USA and Israel. By contrast, the incidence of COVID-19-associated cardiac injury or myocarditis is estimated to be 100 times higher (1,000–1,400 per 100,000 people with COVID-19) than that of COVID-19 mRNA-vaccine-related myocarditis.
A recently published Israeli study described risks for adverse events after mRNA vaccine in comparison with the risks of the same adverse events after infection with SARS-CoV-2. The risk ratio of myocarditis was estimated to increase by a factor of 3.2 after receiving mRNA vaccine, with 1 – 5 events per 100,000 persons. In comparison, the risk of myocarditis was increased by a factor of 18.3 after SARS-COV-2 infection.
Furthermore, COVID-19 associated myocarditis is associated with worse outcomes in patients with pre-existing cardiovascular disease, hypertension and related conditions.
Figure 1: CDC’s extrapolation of predicted covid-19 cases prevented vs myocarditis cases for every million 2nd dose vaccinations over 120 days (Source: US CDC)
Overall, it would seem that despite the inherent risk of vaccine-associated myocarditis, current data presents compelling indications for vaccination. Vaccination strongly reduces the risk of COVID-19-related hospitalisation, intensive care admission and death in both young and elderly individuals.
Diagnosis of myocarditis/pericarditis
Diagnosis is based on the following signs, symptoms and investigations:
- Chest pain
- Shortness of breath
- Feelings of having a fast-beating, fluttering, or pounding heart
- Abnormal ECG
- Raised inflammatory markers (e.g. non-specific C-Reactive Protein, Erythrocyte Sedimentation Rate)
- Raised high-sensitivity cardiac troponin T/I
- Chest X-ray to look out for enlarged heart
- Cardiac Magnetic Resonance Imaging (MRI) for further assessment of structure, function, pericardial and myocardial inflammation and tissue damage
Management
mRNA vaccine-associated myocarditis cases have mostly been benign without significant arrhythmias and with rapid complete spontaneous recovery.
Chest pain can be symptomatically treated with paracetamol or non-steroidal anti-Inflammatory drugs (NSAIDs). In cases of ventricular contractile dysfunction, heart failure treatment such as with angiotensin converting enzyme (ACE) inhibitors and beta blockers can be considered in cases with. In cases with presumed pericardial inflammation, immunomodulatory therapy such as colchicine can be considered. The use of intravenous globulins or corticosteroids should be individually assessed in severe cases.
Recommendations
For patients with a history of pericarditis, it is generally safe to proceed with any FDA-authorised COVID-19 vaccine as long as the heart has fully recovered. As the more serious adverse event following immunisation, patients with a history of myocarditis should be discussed with a cardiologist prior to administering a subsequent COVID-19 vaccine dose.
Figure 2: CDC’s recommendation on vaccines in patients with history of myocarditis or pericarditis
Conclusion
More research will be required to determine long-term outcomes of cardiac inflammation after mRNA vaccines. For now, based on all available current clinical and scientific evidence, the benefits of COVID-19 vaccines by far outweigh the risks.
