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Home » Myocarditis and COVID vaccine – a rare event that may not be linked

Myocarditis and COVID vaccine – a rare event that may not be linked

Regulatory agencies across the world, including the FDA and CDC, are monitoring COVID-19 vaccine adverse events including reports of myocarditis, a heart inflammation. Of course, the anti-vaccine squad will probably jump on this to make it appear that the vaccine is dangerous.

My job is to look at this data and give you a scientific analysis of the observations and whether they are actually related to the vaccine.

Like with reports of other conditions, such as blood clots, after receiving COVID-19 vaccines, we need to examine whether this adverse event is related to the vaccine or just random events in which the incidence is no different than what would be predicted in a similar group of unvaccinated people.

Photo by Robina Weermeijer on Unsplash

What is myocarditis?

Simply, myocarditis, also known as inflammatory cardiomyopathy, is a very rare inflammation of the heart muscle. Symptoms may include shortness of breath, chest pain, decreased ability to exercise, and an irregular heartbeat. The duration of the condition can vary from hours to months. Complications of myocarditis may include heart failure due to dilated cardiomyopathy or cardiac arrest.

Most of the time, myocarditis is caused by an infection that reaches the heart. When it does, the immune cells that fight the infection enter the heart. These immune cells produce biochemicals that can damage the heart muscle. Consequently, the heart itself can become thick, swollen, and weak.

Many of the cases are caused by a virus that reaches the heart. These can include influenza virus (flu), coxsackieviruscytomegalovirus, adenovirus, and others. The condition may also be caused by bacterial infections such as Lyme disease, streptococcus, mycoplasma, and chlamydia.

Myocarditis and COVID vaccine

The CDC’s Advisory Committee on Immunization Practices (ACIP) COVID task force issued a statement on 17 May 2021 that it was examining reports that a few young, predominantly male, vaccine recipients, who had received either the Pfizer or Moderna mRNA vaccines, had developed myocarditis. The CDC said the cases typically occurred within four days after receiving the mRNA vaccines.

CDC monitoring systems have not found more cases than would be expected in the general unvaccinated population. However, members of ACIP felt that healthcare providers should be made aware of the reports of the “potential adverse event.”

Israel’s Health Ministry is also investigating a small number of cases of myocarditis in people who had received Pfizer’s COVID-19 vaccine, though it has not yet drawn any conclusions. A preliminary study showed “tens of incidents” of myocarditis occurring among more than 5 million vaccinated people, primarily after the second dose.

This indicates that less than 2 out of 100,000 may develop this condition. However, published studies show that the risk of myocarditis in the general population is around 22 out of 100,000. In other words, and I cannot stress this enough, the risk of myocarditis is over 10 times greater in the general population than it is in the vaccinated population.

COVID-19 vaccine myocarditis
Photo by Martin Sanchez on Unsplash


Let me repeat myself for the people in the back of the room – the risk of myocarditis is over 10 times higher in the general population than in the population that received the Pfizer COVID-19 vaccine. Furthermore, the risk of death from COVID-19 1000-2000 out of 100,000, nearly 1000X greater than the risk of myocarditis.

For those of you not paying attention, what this story tells me is two things:

  1. The CDC is carefully monitoring adverse events after the COVID-19 vaccine, that’s why it picked up a potential safety signal in myocarditis events. They do this with all vaccines, which contradicts the trope from the anti-vaxxers that no one monitors vaccine adverse events.
  2. Importantly, myocarditis probably is unrelated to the vaccine, but even if it is, the incidence is much lower than the incidence of dying from COVID-19.

I will be monitoring this story if it develops any further, but I just don’t see where there is a link between the COVID-19 vaccines and myocarditis.


  • Cooper LT Jr. Myocarditis. N Engl J Med. 2009 Apr 9;360(15):1526-38. doi: 10.1056/NEJMra0800028. PMID: 19357408; PMCID: PMC5814110.
  • Fung G, Luo H, Qiu Y, Yang D, McManus B. Myocarditis. Circ Res. 2016 Feb 5;118(3):496-514. doi: 10.1161/CIRCRESAHA.115.306573. PMID: 26846643.


Michael Simpson
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