What research shows about the risks of myocarditis from COVID vaccines versus the risks of heart damage from COVID

Frank Han is an assistant professor of pediatric cardiology at the University of Illinois at Chicago And Jennifer H Huang is an associate professor of pediatric cardiology at Oregon Health & Science University.

Shortly after the first COVID-19 vaccines appeared in 2021, reports of rare cases of heart inflammation or myocarditis began to surface.

In most cases, myocarditis was mild and responded well to treatment, although up to four potentially mRNA vaccine-related deaths due to myocarditis in adults have been reported worldwide. No known verified deaths of children have been reported based on publicly available data. The exact number remains a subject of highly heated debate due to the variability in the reporting of possible myocarditis-related deaths.

Studies have largely confirmed that the overall risk of myocarditis is significantly higher after actual COVID-19 infection compared to vaccination, and that the prognosis after vaccine-induced myocarditis is better than after infection. The specific risk of myocarditis varies by age and has been debated due to the differing views of a small group of physicians on risk tolerance and support for or against COVID-19 immunization for specific age groups.

As pediatric cardiologists, we specialize in heart problems relevant to children of all ages. We believe it is important to weigh the risk of myocarditis caused by COVID-19 immunization against not only viral myocarditis due to COVID-19, but also against all other complications that COVID-19 can lead to.

Comparing the risks of myocarditis from serious illness versus COVID-19 vaccination or infection is difficult to do right, and debate continues as to which of those outcomes represents a higher risk.

Myocarditis explained

Myocarditis is any condition that causes inflammation of the heart. A closely related condition called pericarditis refers to inflammation of the outer lining of the heart. For the purposes of this article, we will mainly focus on myocarditis, as it can be a more serious condition. Most cases of myocarditis are caused by infections, especially viral infections.

Myocarditis can be confirmed by a combination of an electrocardiogram, an ultrasound of the heart called an echocardiogram, and some blood tests. When available, cardiac magnetic resonance imaging, or MRI, is the most accurate method of diagnosing myocarditis that does not require an invasive procedure.

A mistaken assumption is that all myocarditis is serious, as it implies damage to the heart. However, mild cases where there is very little swelling and only temporary damage to the heart are more common than severe cases where a machine is needed to support heart function.

Vaccination versus infection risk

The challenge of dissecting the risks of myocarditis from viral infection compared to COVID-19 vaccination is due in part to the difficulty of accurately establishing a diagnosis of myocarditis and population rates.

The United States Vaccine Adverse Event Reporting System, or VAERS — which is an initial reporting system for vaccine adverse events — is not in itself sufficient to determine the rate of a vaccine-associated adverse event. This is because any side effect can be reported and verification of a reported event is only done retrospectively by the Centers for Disease Control and Prevention.

That vetted data is then reported in more robust databases such as the Vaccine Safety Datalink. A very small number of cases of myocarditis following COVID-19 vaccination have resulted in significant long-term sequelae, such as cardiac arrhythmias. However, such cases do not reflect the majority.

Fortunately, severe myocarditis after mRNA vaccination for COVID-19 is extremely rare. A 2021 study by Scandinavian scientists looking at the comparative risks of myocarditis and cardiac arrhythmias in patients who developed myocarditis after COVID-19 infection versus immunization found that the risks differ significantly by age group.

This has been touted as a reason not to vaccinate healthy young men against COVID-19. However, the follow-up study found that the relative risks of adverse outcomes were greater with myocarditis due to COVID-19 infection and other viral myocarditis than with vaccination in all patients over 12 years of age.

And it’s worth noting that as of mid-March 2023, the US is still the world leader in COVID-19 hospitalizations.

Rare cases of myocarditis have also been reported with the newer non-mRNA Novovax vaccine, although we researchers do not yet know the numbers at the population level.

Risk of myocarditis by age and gender

A review of all currently available research shows that the risk of myocarditis following COVID-19 vaccination is highest in young men aged 18 to 39 and older teenage boys aged 12 to 17, with the highest risk following the second dose of vaccine. The cause appears to be related to how the immune system processes the mRNA and sometimes generates an excessive immune response.

The risk of myocarditis associated with COVID-19 immunization is significantly lower in children under age 12 and much lower in adult men over age 50. higher than the risk of myocarditis from COVID-19 vaccination during the pandemic. The risk of myocarditis from vaccination is uniformly lower in girls than in boys.

Babies under 6 months old can only get immunity from their mother’s antibodies unless they are exposed to COVID-19 themselves, as vaccines are not available for this age group.

How to parse the risks

While the risks of myocarditis were highest in teenage boys and young men, regardless of the cause, the severity and outcome of myocarditis after 90 days was much worse when it stemmed from a COVID-19 infection or other viral illnesses. This echoes our team’s research on the same topic.

This discussion also fails to consider the clotting and heart attack risks of COVID-19 itself. Because COVID-19 damages blood vessels in all parts of the body, some organ damage can occur, such as kidney failure, blood clots, heart attacks, and strokes.

We recognize that there is a need for more research into how people fare in the medium and long term following a case of immunization-associated myocarditis. That’s why research is being done, and researchers like us are committed to tracking the data for years to come.

COVID-19 risks in children

Although there are far fewer deaths from COVID-19 in children than in adults, COVID-19 is still one of the leading causes of death among children in the US, according to a survey from early 2023. But COVID-19 deaths are not the only relevant measure of its effect in children. COVID-19 has also killed more children in a shorter period of time than several other vaccine-preventable diseases, such as hepatitis A and meningitis before their vaccines were available.

The argument some have made that fewer children than adults die from COVID-19, or that children often have a mild course, has never been an acceptable justification for not doing everything possible to protect children from it. For example, doctors don’t stop treating pediatric cancer patients just because there are fewer than adult cancer patients. And we’re not stopping measles vaccines just because most kids who get measles only get a mild case.

The primary risk that COVID-19 now poses to children is long COVID, followed by the risk of serious illness. The estimated percentage of children who get long COVID is still debated, but the symptoms of long COVID can be extremely debilitating. These include severe fatigue, brain fog, sleep disturbances, dizziness, nerve pain, and more.

Considering the decision to vaccinate

We believe that the decision to vaccinate against COVID-19 should be based on the patient’s age, other health conditions, the relative risk of vaccines, how much and what type of COVID-19 is prevalent in your community, and patient and family preference.

Two ways suggested by the CDC and the Public Health Agency of Canada to reduce the risk of myocarditis from the COVID-19 vaccine are to opt for Pfizer and delay your doses by at least eight weeks. This is because Pfizer has slightly less myocarditis than Moderna.

Adults who are immunocompromised or have other medical problems known to exacerbate the severity of COVID-19 illness are still at the highest risk of serious illness. They should therefore follow the CDC COVID-19 vaccination schedule with additional boosters if advised by their physician.

While COVID-19 immunizations are now not as efficient at preventing viral transmission as they were with the earliest variety, they remain highly effective at reducing severe illness and hospitalization, even in children, and especially in the high-risk pregnancy.

Fortunately, children have fared much better with COVID-19 infection than adults. The main risks of severe COVID-19 for children are in babies and infants, as well as children with health conditions that put them at high risk, children with the most significant types of congenital heart disease, or children with other medically complex conditions. Children in those groups benefit most from the primary COVID-19 vaccine series; therefore, the decision to vaccinate in their case should be easier.

Informed consent provided with vaccination should include a discussion of infection risks. The risk of immunization will never be zero due to variability in immune system responses; therefore, the most up-to-date information available should always be taken into account when making the decision.

This article has been republished from The conversation under a Creative Commons license.

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