Myocarditis and Covid-19 vaccines: A cardiologist says what you need to know

Conspiracy theories about Covid-19 vaccine side effects are all over the internet and spreading faster than you can say “swollen balls.” But whether real or imagined, concerns about medication side effects and adverse reactions are not unique to Covid-19 vaccines. They also do have a kernel of truth — these vaccines do have side effects. One potential reaction, in particular, merits your attention — especially if you are a younger vaccinated man: Myocarditis.

Myocarditis is when the heart muscle becomes inflamed — a similar condition is pericarditis, which is inflammation of the heart’s outer lining. Both problems are associated with Covid-19 and they are known adverse reactions to the Pfizer-BioNTech and Moderna coronavirus vaccines. These reactions are rare — some data suggest one case may occur in every 172,414 people who get both vaccine doses, but that rate climbs a little higher in men and teenage boys and especially after the second shot.

A June study on the U.S. military had similar findings: 23 service members experienced myocarditis symptoms within days of their Covid-19 vaccine of more than 2 million vaccinated service members — all 23 were male.

Together, these suggest that young men are at higher risk of the unwelcome side effect after the second dose of either of the mRNA Covid-19 vaccines. The potential for heart problems after vaccination has led some countries to limit the use of these vaccines in younger males. The United Kingdom, for example, recommends only kids 12-15 years old get one dose of the Pfizer-BioNTech vaccine.

“Males are more frequently affected than females.”

In the U.S., there is no such recommendation — but young men have a right to understand their risk. Amy Kontorovich, Assistant Professor of Medicine and Cardiology at the Icahn School of Medicine at Mount Sinai, explains to Inverse that while the risk of myocarditis is real, men need to keep one factor in mind when thinking about the vaccines and potential side effects.

The following interview has been lightly edited for house style and clarity.

Inverse: Is myocarditis a side effect of many vaccines?

Dr. Amy Kontorovich: Yes, it has been reported as a complication previously in rare cases following influenza vaccination, and was also reported following smallpox vaccination in military personnel.

Can viruses cause myocarditis?

Yes, the most common cause of myocarditis and pericarditis is a virus — typically the culprits are viruses that are common such as the viruses that cause the common cold or gastrointestinal illnesses.

Are myocarditis and pericarditis both possible complications from the Covid-19 vaccines?

Yes.

Is it true that young men appear to be at risk of developing myocarditis from Covid-19 vaccines?

Of the studies that have reported on myocarditis complications following Covid vaccination, it appears that males are more frequently affected than females. This sex distribution is also what is seen in non-vaccine related, i.e. viral, myocarditis — usually, males are more frequently affected than females.

Are people more likely to get myocarditis from Covid-19 or from the vaccine?

Based on the data at hand at this time, most physicians and public health experts would agree that the risk of serious illness — hospitalization, death — from Covid infection, not to mention post-acute Covid-19 syndrome or “Long Covid,” is significantly higher than the risk of myocarditis for older adults. For this reason, it makes sense for most adults to get vaccinated.

“We are presently lacking scientific evidence to make strong claims about one choice being objectively safer than the other in all children.”

At the other end of the spectrum, the risk of serious illness from Covid infection in most children is extremely low. So it is more fraught to “tolerate” a perhaps higher risk of myocarditis in this age group. I say “perhaps” because we still do not know for sure how the calculation will come out when you try to compare the risk of serious illness from Covid infection to the risk of vaccine-related myocarditis in children. A group of investigators have tried to answer this question and posted their data to a preprint server last month.

The study was criticized for using a specific CDC database [VAERS, a CDC site where people can self-report adverse reactions to the vaccine; those claims eventually need to be verified before they can be trusted] to identify myocarditis cases. [Some have also taken issue with the math in the study.]

The study has not been appropriately vetted through the peer-review process, so it may or may not be flawed — I will wait until it has gone through the peer-review process and published in final form before drawing firm conclusions but the fact of the matter is that we still don’t have the data to fully understand the age-stratified risk of serious outcomes from covid virus vs. vaccine. Any discussion of risk/benefit needs to be made in the context of age. We are presently lacking scientific evidence to make strong claims about one choice (vax kids or not) being objectively safer than the other in all children.

How great is the risk of myocarditis?

The risk signal is notable enough that some countries are tailoring their vaccine recommendations to address this risk-benefit calculation. For example, the UK’s medical advisory board has concluded there is only a “marginal benefit” to vaccinating adolescents on health grounds alone.

The Pfizer vaccine has now been approved in 12-15-year-olds in the UK but they are only going to get one dose. This seems like a reasonable compromise considering that the risk of myocarditis is higher after the second dose. Other countries like Sweden and Denmark have stopped using Moderna in kids under 18 because of the myocarditis risk signal from Pfizer.

A study from Israel on their Pfizer vaccination program reported in the NEJM that the overall incidence of myocarditis for people aged 16 and up was 2.13 per 100,000. However, the incidence was 5 times higher than that in males between ages 16-29.

In terms of the age 5-11 bracket, the Pfizer Phase 2 and 3 clinical trial data have been released by the company — but not yet vetted through the peer-review process. Apparently, there were no myocarditis cases among the 2,268 kids who were vaccinated. Whether that is because these young kids received a lower dose of the vaccine or the sample size was too small to detect such a rare event, or due to differences in young childrens’ immune systems, or other reasons is just not known at this time.

Can Covid-19 damage the heart?

Inverse: What happens to people who develop myocarditis from the Covid-19 virus?

Dr. Amy Kontorovich: Some patients with myocarditis from the Covid-19 virus are experiencing chronic long-term or permanent heart problems, others required mechanical heart support or even transplantation, others died and others made a full recovery.

In one study, the risk of death in patients with Covid-related myocarditis was 1.35 times higher than that in patients who had Covid infection but did not have myocarditis. The more severe the Covid-19 infection was, the worse the outcomes were for patients with myocarditis.

“We simply do not know what the long-term risks are.”

We know from non-Covid studies of viral myocarditis that the overall mortality rate at 5 years follow-up is about 19 percent. It is clearly too early to know whether mortality from myocarditis related to the Covid virus will be similar or different.

What happens to people who develop myocarditis from the Covid-19 vaccine?

We do not have enough data to truly know the outcomes. In the recent Israeli report in the New England Journal of Medicine, they note two patients with death or readmission within roughly 3 months of follow-up among 54 people who had myocarditis from the Pfizer vaccine (3.7 percent). There were 10 patients who had persistent heart muscle damage at the time of hospital discharge; five of these had follow-up testing that found their heart pumping function returned to normal.

Out of a total of 11 people who had follow-up cardiac MRIs, 82 percent had persistent evidence of scar tissue in the heart. So even those with “normal” heart function had abnormal myocardial tissue. The presence of scar tissue in the heart is associated with an increased risk of long-term complications including potentially fatal arrhythmias.

I have seen numerous media characterizations and Twitter threads claiming that “most post-vax myocarditis is mild and patients fully recover.” In my personal experience and that being shared by colleagues, as well as the MRI data above, I do not think this is a complete characterization.

We simply do not know what the long-term risks are.

And it’s worth noting that many of those affected are young people who were previously healthy and are now on three or more heart medications and potentially out of work due to symptoms, even if their heart function is “back to normal.” Ask any advanced heart disease specialist and they will tell you that the measure of heart function, called ejection fraction, doesn’t tell the whole story.

The Inverse analysis — More research is needed to determine the relationship between the Covid-19 vaccines and myocarditis in younger people, especially young men. But if you’re an adult, the science is clear: The benefits of vaccination to prevent and protect against Covid-19 significantly outweigh the very small chance of developing myocarditis as a result of the vaccines.