Myocarditis by the Numbers, Part 1
Health Matters, March 2024

Myocarditis by the Numbers, Part 1

By Caitlin Rothermel

In May 2021, the U.S. Centers for Disease Control and Prevention drafted, but did not publicly share, a national alert describing a link between COVID-19 vaccines and a heart disease called myocarditis. We know about this now because of documents obtained from a Freedom of Information Act request.

Described by the American Heart Association as “serious though rare,” it was estimated in 2014 that 14.4 per 100,000 people in the United States developed myocarditis each year – that’s the same as 1.6 people on our Island of about 11,000.

Myocarditis has become more common with the pandemic. In early 2020, it was first proposed that SARS-CoV-2 infection could lead to myocarditis, and by February 2021, United States physicians were seeing myocarditis cases following the mRNA injections – which had then been on the market for one month. The likely culprit is the spike protein – present on the SARS-CoV2 virus and in the injection, in a modified form. (As always, you can find source documents for this story if you visit us online at

Myocarditis happens when the myocardium – the thick muscle tissue in the middle layer of the heart – becomes inflamed. Pericarditis is a related condition that affects the outer heart layer. Historically in the U.S., the most common cause of myocarditis has been an infectious disease, like a virus. The virus penetrates the heart muscle cells – the myocytes – where it spreads, replicates, and can ultimately kill cells. The immune system is also activated. Progressive myocarditis involves more serious responses, involving chronically inflamed myocytes and/or autoimmune myocyte destruction.

While myocarditis is uncommon, and although it can happen at any age, it has always been a particular risk for younger people, particularly young men. It’s also one of the more common causes of sudden cardiovascular death in competitive athletes. In 2003 in Minnesota, sudden cardiovascular death was shown to occur in 1 in 200,000 high-school athletes. 

Historically, myocarditis has also been caused by vaccines, including smallpox and influenza. And it is accepted medical knowledge that myocarditis can happen after mRNA injections. We were initially and repeatedly advised that injection-delivered spike protein stayed in the arm, but this is not correct. Long Covid research shows that the spike protein can enter circulation and remain there for months after injection, with technology able to distinguish whether the spike protein measured in the body is due to infection or injection.

Right now, we need better clarity on how often post-mRNA injection-related myocarditis occurs, and what this means for us and our young people. The U.S Centers for Disease Control labels the condition as “rare.” Two recently published reviews estimate that cases are at 0.3 to 5.0 per 100,000, as seen in the ≤41 days following injection.

Already, with these numbers, we are in uncharted territory in terms of what’s considered an acceptable safety profile. Our threshold for risk was once much lower: In 1976, the Swine Flu vaccine was pulled from the U.S. market because of 1 additional case per 100,000 of Guillain-Barrè Syndrome, a potentially serious neurologic disease. 

When considering these myocarditis case rates of 0.3 to 5.0, it’s important to remember that this is an averaged risk for everyone – including people at very low risk. So, these numbers don’t address our primary, societal concern. The risk story changes a lot when you look at young men, especially after the second injection: 

In an evaluation of four Nordic countries, 9 to 28 additional myocarditis cases were seen per 100,000 men (aged 16 to 24 years); case numbers in two national studies from Israel (also per 100,000 men) were 15.1 (16-19 years) and 5.5 to 18.4 (16-29 years). So, in twice-injected young men, the number of myocarditis events may be more than double what we have been told to expect for people overall.  

Most recently, two new studies have received substantial national attention. Just published, the “99 million” Global COVID Vaccine Safety Project looked at how often 13 types of adverse events happened in the 42 days after injection. The study was thorough: It included 10 sites in 8 countries, and the sites did independent research to determine their local rates of myocarditis in the years before COVID – this made for a clear “before” and “after” story. 

Of all events studied, myocarditis and pericarditis consistently had highest safety risk after the first and second mRNA injections. News sources have reported that this increased risk was “small” or “slight,” but in fact, this analysis found that myocarditis and pericarditis after injection are now happening 2 to 7 times more often than what was normal in the past. In this case, these data are for everyone, not just young men (this study didn’t report the numbers by patient age). 

There is more to say, but too much to say about myocarditis to cover in one article. Next month, we will look at the second new myocarditis publication. It studied events reported to our national vaccine database tracking system and compared post-COVID numbers to historical patterns. We will also dive deeper into the evidence behind widely stated claims that the benefits of the injection “outweigh the risks,” and that myocarditis rates are actually higher following COVID infection.

March 7, 2024

About Author

caitlin I’m a member of the Vashon Loop Editorial Board and write about medicine, health, and society. I’m a research geek and an MPH, and I’m also a mom, farmer, teacher, and apocalypse librarian. I edit things. If I’m not doing something, it’s probably because I am asleep.