COVID-19 shots and Myocarditis: Clearing the Confusion

This week Melody explains how we know that getting myocarditis from COVID-19 is more dangerous than getting myocarditis from the COVID-19 vaccine.

Got a question for Melody?

A US government report on COVID-19 vaccine safety has put the link between myocarditis and the mRNA vaccines back in the news. One of our readers asks if the vaccines make myocarditis more dangerous or just more likely. 

Dear Melody, 

Medical News Bulletin recently had an article about COVID-19 vaccine side effects. I got from the report that the vaccine made myocarditis more likely, but I saw loads of headlines saying myocarditis was less severe. Which is it? What’s the difference? 

Regards,

Skeptic Reader

Dear Skeptic Reader,

In rare cases, there is a link between mRNA-based COVID-19 vaccination and inflammation of the heart (myocarditis), but you are 50 times more likely to die with myocarditis triggered by COVID-19 than from myocarditis triggered by a COVID-19 vaccine. 

A regular person who developed myocarditis would have a 1% risk of dying. If the myocarditis was caused by COVID-19, that risk of death shoots up to 10-20%. 

If, on the other hand, the myocarditis was prompted by an mRNA vaccination…your risk of dying is actually the lowest at less than 0.5%.

What’s more, the mRNA vaccines don’t have a huge effect on your chances of developing inflammation in and around your heart either. Stats collected by healthcare systems across the world show that there is a tiny increase in the risk of myocarditis after vaccination — 1.2  more cases than normal per million vaccinations.^1-3 

A report by the United States’ National Academy of Sciences on the safety and effectiveness of COVID-19 vaccines found that only mRNA-based vaccines were linked to myocarditis. If this is something you are concerned about, vaccines based on other technologies are also widely available, for example the current Canadian COVID-19 vaccines page lists adenovirus-based vaccines.⁴

Having a “higher risk” of myocarditis after vaccination, means that there’s more of a chance or likelihood of developing it. This is different from saying the myocarditis itself will be more severe or worse. It does not mean the myocarditis would be more serious or hard to treat. The reality is, the vast majority of myocarditis cases linked to vaccination were mild and resolved quickly with rest and treatment.^1-11

So what caused the confusion?

The recent Medical News Bulletin article our reader cited summarized a report by the United States’ National Academy of Sciences on the safety and effectiveness of COVID-19 vaccines. The report concluded that the benefits of getting vaccinated far outweigh the risks. 

While some adverse events were reported, they were uncommon and less severe than the effects of COVID-19. In this report the US senior scientists investigated whether the various different COVID vaccines had side effects or made people sick. Although the report focused on the chances a person would experience a symptom, and whether the vaccine caused it, the report did not look at outcomes. This means they did not say whether a side effect was bad or dangerous, just that it had been reported.

What the research tells us about Myocarditis and COVID-19

Meta-analyses, such as the 2022 study from the University of Oxford, reveal a stark difference in the mortality risk associated with myocarditis triggered by COVID-19 infection versus vaccination.¹² While myocarditis generally carries a 2% mortality rate, this figure jumps to a concerning 13% when linked to COVID-19.^3,12

In contrast, the mortality rate for vaccine-induced myocarditis stands at a much lower 0.44%.^3,12 Experts suggest this may be partly due to the demographic most affected by severe vaccine-induced myocarditis: teen boys, who generally have a lower risk of complications.^3,7

What causes myocarditis? 

Myocarditis happens when the muscle cells that make up your heart react to danger. They release enzymes that fight off infection and repair injuries. This can cause swelling, making it harder to pump blood and it can make it difficult for the cells to contract in the right rhythm. It can be caused by viral infections (like COVID-19), bacterial infections, autoimmune diseases, and certain medications. The severity varies significantly depending on the underlying cause, the patient’s age, their overall health, and how fast they get treatment.

When myocarditis is triggered by a COVID-19 infection, it tends to be more severe than normal, with more chance of complications and even death.

The takeaway is clear: while vaccination carries a slight increase in myocarditis risk, the severity and mortality rate associated with it pale in comparison to myocarditis triggered by COVID-19 infection. The data underscores the importance of vaccination in mitigating the potentially devastating consequences of COVID-19.

According to the CDC, myocarditis (heart muscle inflammation) following COVID-19 vaccination is rare.⁵ Multiple studies and safety monitoring systems around the world have reported that certain vaccines can, in rare cases, provoke myocarditis.⁶ This doesn’t mean everyone who gets vaccinated will develop these conditions. Rather, it indicates that vaccines based on mRNA technology can sometimes trigger myocarditis, but other factors likely play a role too.

Sincerely,

Editor

References

1. Vaers Home (no date) VAERS. Available at: https://vaers.hhs.gov/about.html (Accessed: 20 September 2024). 
2. Ling RR, Ramanathan K, Tan FL, Tai BC, Somani J, Fisher D, MacLaren G. Myopericarditis following COVID-19 vaccination and non-COVID-19 vaccination: a systematic review and meta-analysis. Lancet Respir Med. 2022 Jul;10(7):679-688. doi: 10.1016/S2213-2600(22)00059-5. Epub 2022 Apr 11. Erratum in: Lancet Respir Med. 2022 Jul;10(7):e72. doi: 10.1016/S2213-2600(22)00176-X. PMID: 35421376; PMCID: PMC9000914.
3. Bemtgen, X. et al. (2022) ‘Myocarditis mortality with and without COVID-19: Insights from a national registry’, Clinical Research in Cardiology, 113(2), pp. 216–222. doi:10.1007/s00392-022-02141-9. 
4. Canada, H. (2024) Government of Canada, Canada.ca. Available at: https://www.canada.ca/en/health-canada/services/drugs-health-products/covid19-industry/drugs-vaccines-treatments/vaccines/type-viral-vector.html (Accessed: 23 September 2024). 
5. Myocarditis and pericarditis after mrna COVID-19 vaccination (no date) Centers for Disease Control and Prevention. Available at: https://www.cdc.gov/coronavirus/2019-ncov/vaccines/safety/myocarditis.html (Accessed: 07 September 2024). 
6. Clinical considerations: Myocarditis after covid-19 vaccines (2023) Centers for Disease Control and Prevention. Available at: https://www.cdc.gov/vaccines/covid-19/clinical-considerations/myocarditis.html (Accessed: 20 September 2024). 
7. Oster ME, Shay DK, Su JR, Gee J, Creech CB, Broder KR, Edwards K, Soslow JH, Dendy JM, Schlaudecker E, Lang SM, Barnett ED, Ruberg FL, Smith MJ, Campbell MJ, Lopes RD, Sperling LS, Baumblatt JA, Thompson DL, Marquez PL, Strid P, Woo J, Pugsley R, Reagan-Steiner S, DeStefano F, Shimabukuro TT. Myocarditis Cases Reported After mRNA-Based COVID-19 Vaccination in the US From December 2020 to August 2021. JAMA. 2022 Jan 25;327(4):331-340. doi: 10.1001/jama.2021.24110. PMID: 35076665; PMCID: PMC8790664.
8. Bürgi JJ, Rösslein M, Nolte O, Wick P, Garcia Boy R, Stranders S, Dollenmaier G, Peier K, Nohynek B, Fischer A, Stolz R, Cettuzzi M, Graf L, Korte W. Mild COVID-19 induces early, quantifiable, persistent troponin I elevations in elder men. Front Cardiovasc Med. 2022 Dec 1;9:1053790. doi: 10.3389/fcvm.2022.1053790. PMID: 36531721; PMCID: PMC9751190.
9. Paruchuri SSH, Farwa UE, Jabeen S, Pamecha S, Shan Z, Parekh R, Lakkimsetti M, Alamin E, Sharma V, Haider S, Khan J, Razzaq W. Myocarditis and Myocardial Injury in Long COVID Syndrome: A Comprehensive Review of the Literature. Cureus. 2023 Jul 25;15(7):e42444. doi: 10.7759/cureus.42444. PMID: 37637608; PMCID: PMC10449234.
10. Fairweather, D. et al. (2023) ‘Covid-19, myocarditis and pericarditis’, Circulation Research, 132(10), pp. 1302–1319. doi:10.1161/circresaha.123.321878. 
11. Association between COVID-19 and myocarditis using hospital-based administrative data – United States, March 2020–January 2021 (2021) Centers for Disease Control and Prevention. Available at: https://www.cdc.gov/mmwr/volumes/70/wr/mm7035e5.htm (Accessed: 20 September 2024). 
12. Patone, M. et al. (2022) ‘Risk of myocarditis after sequential doses of COVID-19 vaccine and SARS-COV-2 infection by age and sex’, Circulation, 146(10), pp. 743–754. doi:10.1161/circulationaha.122.059970. 
13. Rottmann, F.A. et al. (2024) ‘Myocarditis incidence and hospital mortality from 2007 to 2022: Insights from a nationwide registry’, Clinical Research in Cardiology [Preprint]. doi:10.1007/s00392-024-02494-3.