Understanding the Latest Data on Vaccine Triggered Heart Issues

Sam Westreich, PhD

Don’t panic. This is new data on vaccine risks — but it’s important to keep in perspective.

COVID vaccines may increase your risk of heart inflammation, but that’s better than massive lung damage.Photo byPhoto by Olivier Collet on UnsplashonUnsplash

There’s been an alarming amount of science skepticism in recent years. When vaccines rolled out for COVID-19, we should have been celebrating that we had a solution to a disease that killed more than 6.7 million people in the last 3 years.

Instead, we’ve seen a significant amount of vaccine fear and skepticism, with arguments focusing on everything from its effectiveness (“if you get vaccinated, you still can get COVID, so what’s the point?”) to potential side effects (“Vaccines make you sick, or cause heart problems!”).

These fears aren’t totally unfounded. This is the largest-scale rollout of a vaccine that uses mRNA, rather than a neutralized viral particle, in order to generate immunity. And these vaccines were deployed quickly, thanks to the acceleration of President Trump’s Operation Warp Speed effort.

Unfortunately, fears tend to move faster than scientific reassurances. Science, after all, requires data, while fear requires nothing more than the “Share” or “Retweet” button.

So it wasn’t until January of this year, 2023, that a paper was published in Circulation, a journal of the American Heart Association, discussing the detection of a COVID protein in patients with heart inflammation.

But this protein wasn’t from an infection. It was from the vaccine.

Should we be worried? Does this mean that the COVID vaccine is dangerous, after all?

Before we panic, let’s look at what the paper — and other scientific data — tells us.

What this research report found

First, the paper itself is more of a report, rather than an experiment. The authors examined the blood of patients who experienced myocarditis (inflammation of the heart) or pericarditis (inflammation or swelling of the pericardium, the thin sac that surrounds the heart). They specifically focused on adolescents and young adults, people who usually don’t show up with heart problems.

In the blood of the 16 cases that they found, they noted that there were elevated levels of the COVID-19 spike protein circulating, unbound by antibodies. This is the protein that is created, indirectly, by the COVID mRNA vaccines.

A quick note on how mRNA vaccines work, versus traditional ones:

  • Traditional vaccines contain a chunk of the virus, either a piece of the virus or an entire dead virus. This gets injected so that our immune system learns how to recognize and destroy any future viruses that match the dead pieces.
  • mRNA vaccines work by providing a piece of RNA that instructs our own cells to make a viral protein. That viral protein is recognized by our immune system, so it learns to destroy any future viruses with that piece. It’s much faster to make mRNA vaccines, because it’s much faster to make these RNA blueprints than to procure large amounts of dead virus.

The researchers state that myocarditis is a fairly rare occurrence in vaccinated individuals; it seems to occur in 1–2 people for every 100,000 who are vaccinated (0.0015%).

Some interesting notes:

  • Of the 16 individuals who presented with myocarditis or pericarditis, 13 of them (81%) were male.
  • 12 of the individuals developed inflammation after the 2nd dose; 2 were after the 1st dose and 2 were after the 3rd dose of vaccine.
  • The affected individuals didn’t show any overall abnormalities with their immune systems.
  • Even the affected individuals showed greatly improved COVID immunity.

What, specifically, causes the myocarditis? The researchers propose that it’s the spike protein, rather than being due to the vaccine being mRNA-based. The spike protein shows some ability to evade the immune system, and myocarditis has occasionally occurred with other vaccines (that aren’t for COVID and aren’t mRNA-based).

In these individuals, the immune system doesn’t seem to be able to catch all the spike protein, and so it remains circulating and may go on to trigger heart inflammation.

What’s the broader context? How should we interpret this?

If you’re still reading this, you hopefully aren’t panicking and urging everyone to cancel any upcoming COVID booster appointments. That’s good. Don’t panic.

Our most important consideration, and the way we ultimately make decisions, is based on relative risk. It’s why we still get prescriptions for drugs, despite a long list of potential side effects; most of us are willing to risk a 0.1% chance of serious diarrhea in exchange for a near-guaranteed reduction of high blood pressure.

Myocarditis doesn’t seem to be a condition caused by COVID itself. An Israeli paper looked at nearly 200,000 (non-vaccinated) COVID patients and healthy controls, examining rates of myocarditis and pericarditis. They found:

Nine post-COVID-19 patients developed myocarditis (0.0046%), and eleven patients were diagnosed with pericarditis (0.0056%). In the control cohort, 27 patients had myocarditis (0.0046%) and 52 had pericarditis (0.0088%).

Their results show that you’re more likely to develop myocarditis if you’re male, but COVID itself doesn’t increase your chances. This may be because, in a real COVID infection, the spike protein is attached to the rest of the virus and not circulating freely.

This is still up for debate, however, as some other papers suggest that in young males (the most vulnerable group for myocarditis), COVID infection has a 6x greater rate of causing myocarditis compared to the vaccine.

However, most cases of myocarditis are not life-threatening. They usually do not last long or cause permanent damage, and generally abate within a few weeks. In fact, in a follow-up of 519 individuals who reported vaccine-associated myocarditis, only 1% reported worsening cardiac status while >95% reported improvement at 90 days post-diagnosis.

On the other hand, a COVID infection, especially in a non-vaccinated individual, can be life-threatening and has the potential to do far more damage.

Even the authors of this paper agree, in their conclusion:

Although the implications of this finding must be better understood, these results do not alter the risk-benefit ratio favoring vaccination against COVID-19 to prevent severe clinical outcomes.

The best move now is to get a COVID booster

Vaccine skeptics have accused the medical establishment of moving the goalposts, with arguments that the vaccine puts you at risk of all sorts of side effects, without granting immunity to COVID.

While it is true that the vaccine does not completely prevent someone from getting COVID, it’s been widely shown that COVID in vaccinated individuals is far less dangerous than in unvaccinated individuals. Vaccination’s protected status does not last forever, and the original vaccines are not as well suited to the newer variants of COVID.

This latest paper, even focused on a very small cohort of individuals, suggests that the risks of the COVID vaccine are minor and rare. The vaccine does carry a risk of myocarditis (heart inflammation), but the condition is not life-threatening in greater than 95% of cases.

Overall, the mortality rate of COVID in adolescents, especially men under the age of 40, is low — but so are the risks of the vaccine. And vaccinated individuals are far more likely to have a much milder case of COVID, which in turn reduces the chances of spreading the disease to other, more vulnerable members of the community.


In conclusion, this latest study reaffirms much of what we already know: the COVID vaccine, like other vaccines, carries a small chance of causing mild heart inflammation, or myocarditis. Men under the age of 40 were at greatest risk of myocarditis, but nearly all of them recovered within 90 days.

This presents a minor risk, but even the authors of the study agree: the best choice is still to get vaccinated, and to receive the bivalent booster (protects against both Omicron and original flavor COVID!) as soon as possible.


Want to subscribe to NewsBreak for all the most up-to-date news? Click here.

Want to earn money by writing for NewsBreak? Sign up here.

Comments / 1330

Published by

A microbiome scientist working at a tech startup in Silicon Valley, Sam Westreich provides insights into science and technology, exploring the strangest areas of biology, science, and biotechnology.

Mountain View, CA

More from Sam Westreich, PhD

Comments / 0