Findings from researchers in Basel didn’t show an 800-fold increase in myocarditis in vaccinated people compared to unvaccinated individuals

Key takeaway

Multiple scientific studies show that COVID-19 vaccines effectively reduce the risk of severe disease and death. Observations from researchers in Basel using a more sensitive detection protocols revealed that there are cases of mild myocarditis that previously went undetected owing to the absence of severe symptoms. The risk of myocarditis requiring medical attention is higher during COVID-19 than after vaccination with mRNA vaccines.

Reviewed content

Verdict:

Inaccurate

Claim:

“The risk of myocarditis is 800 times higher for vaccinated than unvaccinated young adults, according to a recent Swiss study”

Verdict detail

Misrepresents source: The findings by Müller and colleagues showed that the incidence of vaccine-associated myocarditis was higher than previously reported when cases were identified using a more sensitive method instead of only counting myocarditis cases requiring medical attention. It didn’t compare myocarditis incidence between vaccinated and unvaccinated individuals.
Overstates the scientific impact of a finding: The results from Müller and colleagues alone are insufficient to update current recommendations on vaccine use. The research didn’t include a control group nor measure the baseline amount of troponin in participants before vaccination. It also didn’t investigate whether and how often such mild myocarditis cases were associated with COVID-19.

See our method of evaluation

Full Claim

“The risk of myocarditis is 800 times higher for vaccinated than unvaccinated young adults, according to a recent Swiss study”

After the onset of mass COVID-19 vaccination campaigns against COVID-19, public health agencies worldwide began to detect rare cases of myocarditis, a type of heart inflammation, among people who had received one of the authorized COVID-19 mRNA vaccines.

This discovery became fodder for a number of inaccurate claims about the risks of mRNA vaccines, which Health Feedback refuted on several occasions. And new scientific results on COVID-19 vaccines and myocarditis continue being misrepresented in a way that casts doubt on the vaccines’ safety.

An example of this is the claim that a new study from a Swiss team showed that “the risk of myocarditis is 800 times higher for vaccinated than unvaccinated young adults”. An alternative version of the claim reads “Covid shots increase risk of myocarditis by 800 TIMES in young adults”.

However, this misrepresents and exaggerates the findings of a team of researchers at Basel University and University Hospital Basel. Firstly, the findings that the claim refers to were communicated during a presentation given by Christian Müller, a professor of cardiology at Basel University, at the European Society of Cardiology Congress in August 2022. The findings have yet to be published in a peer-reviewed journal, therefore describing this set of results as a “study” is inaccurate and misleading.

Secondly, contrary to the claim, the researchers didn’t compare vaccinated people with unvaccinated people. Rather, it showed that using a more sensitive method to detect myocarditis increased the number of myocarditis cases detected, which is as expected. We provide more details below.

Myocarditis is an inflammation of the heart muscle. This can damage its structure and hamper its ability to pump blood. A common cause of myocarditis are bacterial or viral infections, including SARS-CoV-2. When COVID-19 causes myocarditis, it usually leads to a poorer COVID-19 prognosis, meaning that the patient is at higher risk of a bad outcome from the disease^[1,2].

COVID-19 mRNA vaccines are also associated with myocarditis. However, clinical evidence so far indicates that the risk of developing myocarditis that requires medical attention is lower after vaccination than after COVID-19 itself^[3-7].

To understand why the claim is inaccurate, we first need to explain what the research from Basel University mentioned above did and understand what sets it apart from published studies.

In this research, scientists prospectively monitored the heart condition of people who received a booster shot of COVID-19 mRNA vaccines. This is in contrast to published studies on vaccine-associated myocarditis, which usually relied on medical records or health insurance data to detect such cases.

The weakness of such studies is that they can only detect myocarditis cases that require medical attention. If COVID-19 vaccination also caused cases of myocarditis so mild that they didn’t require medical attention, these studies wouldn’t have been able to detect them. The team led by Müller addressed this potential gap in knowledge by detecting heart injury via blood troponin measurements days following a COVID-19 booster shot. Troponin is a type of protein found in heart muscle. When cardiac muscle is damaged, troponin leaks into the blood and can be detected using a blood test.

Elevated troponin in the blood can happen for many reasons, which can be serious or benign, ranging from a heart attack, heart failure, renal failure, myocarditis, heart transplant, and even strenuous exercise^[8]. When all other plausible explanations are eliminated, an elevated troponin level after the booster shot is thus likely to have been caused by the vaccination and would suggest a mild cardiac injury.

The researchers found that 2.8% of individuals had an above-average level of troponin at day three after vaccination. In an interview published by Basel University, Müller stated that this is 800 times higher than the 0.0035% reported by previous studies on vaccine-associated myocarditis. Müller didn’t provide a source for the figure of 0.0035%, but it is within the range of incidences reported by others^[3].

Contrary to the claim, this 800-fold increase arises from comparing the analysis of Müller et al. on vaccinated individuals to previous studies also on vaccinated individuals. It doesn’t compare vaccinated and unvaccinated people.

In the interview, Müller explained: “From the earlier, passive observation of the severe cases, it was concluded that out of 1,000,000 vaccinated people, about 35 develop an inflammation of the heart muscle. In our study, we found evidence of mild, temporary cardiac muscle cell damage in 22 of the 777 participants, i.e. 2.8 percent instead of the expected 0.0035 percent” [emphasis added].

Therefore, the results from Müller’s team tell us nothing about how much more often vaccinated people develop myocarditis compared to unvaccinated people, contrary to the claim.

Health Feedback reached out to Müller for comment on this claim but didn’t receive a response by the time of publication.

Furthermore, the research has several limitations that preclude drawing any new conclusions on vaccine safety or vaccine use recommendations.

First, the research didn’t include a control group that didn’t receive the booster shot. It also didn’t include a measurement of the baseline level of troponin in the blood before the vaccination. Therefore, we don’t know whether troponin levels were already elevated in some people before vaccination.

Second, the data we do have show that the risk of myocarditis is higher during COVID-19 than after vaccination. It’s unclear how much the findings of Müller et al. change our current understanding of these risks. As Müller explained in the Basel University interview, the study didn’t use the same method to investigate the incidence of myocarditis in COVID-19 patients. Therefore, there’s not enough information to compare COVID-19 patients with vaccinated people.

What these results essentially tell us is that using a more sensitive approach for detecting myocarditis leads researchers to detect more myocarditis cases, which is as expected. It is plausible that using the same approach in patients with COVID-19 would also increase the number of detected myocarditis cases and as a result lead researchers to report a much higher incidence of COVID-19-associated myocarditis.

As Müller highlighted in the interview, “[T]his is about mild effects”. What the medical consequences of these mild myocarditis cases are is unknown. Therefore, these results alone are insufficient for changing the current vaccine recommendations. Müller emphasized that the COVID-19 vaccines have provided great public health benefits, stating, “Without this development, the pandemic damage would have been several orders of magnitude higher. The vaccines have saved millions of lives.”

UPDATE (30 Nov. 2022):

The text was updated to improve clarity, in particular, the fact that the research from Müller et al. was communicated through a presentation in a scientific meeting and not in a peer-reviewed study.

REFERENCES

• 1 – Castiello et al. (2022) COVID-19 and myocarditis: a systematic review and overview of current challenges. Heart failure review.
• 2 – Buckley et al. (2021) Prevalence and clinical outcomes of myocarditis and pericarditis in 718,365 COVID-19 patients. European Journal of Clinical Investigation.
• 3 – Heymans & Cooper (2021) Myocarditis after COVID-19 mRNA vaccination: clinical observations and potential mechanisms. Nature reviews cardiology.
• 4 – Boehmer et al. (2021) Association Between COVID-19 and Myocarditis Using Hospital-Based Administrative Data — United States, March 2020–January 2021. Morbidity and mortality weekly review.
• 5 – Wong et al. (2022) Risk of myocarditis and pericarditis after the COVID-19 mRNA vaccination in the USA: a cohort study in claims databases. The lancet.
• 6 – Voleti et al. (2022) Myocarditis in SARS-CoV-2 infection vs. COVID-19 vaccination: A systematic review and meta-analysis. Frontiers in cardiovascular research.
• 7 – Pantone et al. (2022) Risk of Myocarditis After Sequential Doses of COVID-19 Vaccine and SARS-CoV-2 Infection by Age and Sex. Circulation.
• 8 – Korff et al. (2006) Differential diagnosis of elevated troponins. Heart.