What is currently known about myocarditis and the Comirnaty vaccine?

A statement from the WHO Global Advisory Committee on Vaccine Safety on 9th July 2021 noted that clinicians need to be aware of the risks of myocarditis and pericarditis following mRNA vaccination and those most likely to be affected. Presentation includes acute chest pain, shortness of breath and palpitations, especially in young males.

Since April, increased reports of myocarditis or pericarditis being diagnosed in the few days following receipt of Comirnaty vaccine, particularly following the second dose and in younger males, were being noted in countries with the largest number of vaccine recipients aged under 30 years, initially in Israel and the much larger US population.

Based on confirmed cases reported VAERS (passive surveillance system equivalent of CARM in the US), the incidence of myocarditis or pericarditis in young men aged 12-29 years was approximately 40 cases per million second doses of an mRNA vaccine (or 1 in 25,000). Case in young women were around 10-fold lower (4.2 cases per million or 1 in 250,000). The incidence in those aged over 30 years is lower again (about 1 in 400,000 in males and 1 per million in females). Although about 90% of the 303 confirmed cases of myocarditis reported to the US CDC occurring following mRNA vaccination were hospitalised, as of 23 June, 95% had been discharged from hospital and 81% were fully recovered.

Myocarditis and pericarditis are uncommon conditions, usually thought to be related to viral infection leading to inflammation of the heart muscle or the tissue surrounding the heart. Chest pain is the most common symptom. Diagnosis is based on elevated levels of cardiac enzymes (troponin) and specific cardiac tests of electrical activity (ECG) and structure (echocardiogram). Rates of incidence vary between populations and by gender and age; for example, the incidence in adolescent males aged 14 to 18 years is consistently higher than in females. Estimates of how common these occur depend on how carefully the diagnosis is being looked for.

It is important to rule out other potential causes of myocarditis, such as viral infections including COVID-19, or rheumatological causes. Suspected cases should be evaluated, provided guidance and followed up by a consultant cardiologist.

Report all such cases to CARM. MedSafe is closely monitoring for any reports of myocarditis following COVID-19 vaccination in New Zealand. See WHO statement here:

Webinar replay: The mRNA COVID-19 vaccine in NZ: understanding variants and safety signals including myocarditis

20 July 2021: This webinar covers vaccine effectiveness with COVID-19 variants and current information around vaccine safety.

Presenters: Dr Joan Ingram & Dr Peter McIntyre, Medical Advisors for the Immunisation Advisory Centre

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