Evidence suggests myocarditis risk after Covid-19 vaccination is lower compared to Covid infection

21 December 2021

A video posted on Facebook claims myocarditis is more dangerous if you catch it following Covid-19 vaccination than from a Covid-19 infection. 

The video, taken from a longer interview with American cardiologist Dr Peter A. McCullough, also claims that vaccine-acquired myocarditis in children is “way more serious and more prominent than a post-Covid (infection)” with 90% requiring hospitalisation. 

However, while the evidence on this is limited, what we do have suggests the risks from this inflammatory heart condition are actually greater after a Covid-19 infection compared to post-vaccine. 

Myocarditis is inflammation of the heart muscle and while most people recover from it, it can cause severe heart damage.

Are you at greater risk from myocarditis if you’re vaccinated?

In the video, Dr McCullough says myocarditis following infection is “inconsequential” and not like “what we’re seeing with the vaccines.”

This is not what current research suggests. 

Although there have been reported cases of myocarditis caused by vaccines and Covid infections, evidence shows the risk of experiencing myocarditis from both infection and vaccination is small. A recent study found that “there was an increase in the risk of myocarditis within a week of receiving the first dose of both adenovirus and mRNA vaccines, and a higher increased risk after the second dose of both mRNA vaccines.” It also concluded that “in the same population, there was a greater risk of myocarditis […] following SARS-CoV-2 infection.” 

A study published in September assessing the safety of the Pfizer vaccine found that while there was an “excess risk” of myocarditis among vaccinated subjects (around three events recorded per 100,000 people) this was far lower than the risk among those who had been infected with Covid (11 events recorded per 100,000 people).

Another study assessed 718,365 Covid-19 patients and of these 35,820 developed new-onset myocarditis. In this group 3.9% died from any cause within six months compared to 2.9% in the control group without myocarditis, with higher associated odds of rehospitalization and heart attacks. 

Research published in December 2021 found that among 2.5 million vaccinated people, only 54 met the study’s criteria for myocarditis. That’s around two cases per 100,000 and 76% of these cases were described as mild.

The Medicines and Healthcare products Regulatory Agency (MHRA) has recorded 789 Yellow Card reports of myocarditis following vaccination (as well as a handful of other types of myocarditis reported, for example viral myocarditis). There have been reports of five deaths linked to inflammatory heart conditions. The MHRA says symptoms are “typically mild with individuals usually recovering within a short time with standard treatment and rest.” 

It also adds: “The nature of Yellow Card reporting means that reported events are not always proven side effects. Some events may have happened anyway, regardless of vaccination.”

What about the risk in children?

Later in the video, Dr McCullough suggests that the risks of myocarditis in children are “way more serious and more prominent than post-Covid (infection)”.

It’s worth noting that there is not a lot of evidence on the risk of clinical outcomes of children with myocarditis caused by Covid-19 infections and even less on its association with vaccines. This may be in part due to the relative infancy of Covid-19 and the even more recent rollout of its vaccines among younger age groups. 

Recent data from the US Centres for Disease Control and Prevention showed that of over seven million doses of the Pfizer vaccine administered to children aged five to 11, there were eight reports of adverse reactions which met the “myocarditis case definition”.

Currently, in the UK only children aged 12 and older can be vaccinated. 

However, what evidence does exist for this age group suggests the risk of myocarditis is higher following Covid-19 infection and the clinical outcomes may be worse. 

One piece of pre-print research has compared the clinical outcomes in children with “classic viral” myocarditis to those with myocarditis linked to an inflammatory condition seen in some children after Covid-19 infection and myocarditis linked to vaccines. Out of 201 patients, 43 had classic myocarditis, 149 had myocarditis linked to the inflammatory condition and nine had Covid-19 vaccine-acquired myocarditis. 

The researchers found that compared with “classic viral” patients, those with myocarditis linked to the inflammatory condition experienced more significant instances of blood disorders and worse inflammation when first seen by clinicians (although they had better clinical outcomes than “classic viral patients”). Patients diagnosed with myocarditis linked to the inflammatory condition or vaccination both showed prompt recovery from symptoms and improvement of cardiac function.

Another study, released in December 2021 assessed 140 episodes of confirmed or probable myocarditis following vaccination among adolescents and young adults. It found 19% of patients were sent to intensive care. None, however, died or required extracorporeal membrane oxygenation treatment, or Ecmo, where blood is cycled through an artificial lung machine before returning it to the body. The study concluded that “most cases of suspected COVID-19 vaccine myocarditis occurring in [people under 21] have a mild clinical course with rapid resolution of symptoms.”

A preprint study (which has not been peer reviewed) published in July assessed the risk of myocarditis after a Covid infection in under 20s based on more than 34,000 medical records. In males between 12 to 17-years old, there were 450 cases of myocarditis per million infections after adjustment for missed cases and infections. For females in the same age group there were 213 per million cases.

No evidence for troponin level claims 

During the video, Dr McCullough says that levels of troponins (a protein released into the bloodstream that can detect myocardial injury) are “10 to 100 fold times higher” in patients that acquire myocarditis following vaccination, compared to those who acquire it after an infection.

Professor Saidi Mohiddin, professor of cardiology at Barts Health Centre & Queen Mary University of London, told Full Fact via the Science Media Centre  that “troponin elevation in post covid myocarditis can be as high or higher as that in post vaccine myocarditis”. 

He added: “In the relatively rare cases where patients develop clinically relevant acute myocarditis due to Covid-19 infection, troponin elevation can be dramatic, its magnitude reflecting the greater extent of myocardial injury. 

“This, moreover, is true regardless of the cause of myocarditis: troponin elevation is a well-recognised abnormality in acute forms of myocarditis, long before Covid-19 or RNA vaccines were on the scene.”

Do lipid nanoparticles attack the heart?

Dr McCullough also says there are preclinical studies which suggest lipid nanoparticles, (small structures that have an outer layer made of fat that doesn’t dissolve in water that protect the delivery of mRNA in the vaccines), “go right into the heart, the heart expresses the spike protein (and) the body attacks the heart”

There is no evidence of this. A paper published in the cardiology journal Circulation on myocarditis and Covid-19 vaccination states: “Lipid nanoparticles or adjuvants used in mRNA vaccines have not been shown to result in an immune or inflammatory response and have not been associated with myocarditis either.”

Terrence Wilkins, emeritus professor of nanomanufacturing innovation at the University of Leeds, agreed with the findings in Circulation and said it is also what he would have expected based on previous work his team had done.

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