Researchers compare the risk of myocarditis between Pfizer and Moderna COVID-19 vaccines

Incidence of myocarditis, pericarditis or myopericarditis is two- to threefold higher after a second dose of the Moderna Spikevax COVID-19 vaccine when compared to the Pfizer BioNTech COVID-19 vaccine; however, overall cases of heart inflammation with either vaccine are very rare, according to a study in the Journal of the American College of Cardiology. The study showed males younger than 40 years old who received the Moderna vaccine were shown to have the highest rates of myocarditis, which according to the authors, may have implications for choosing specific vaccines for certain populations.

Two mRNA COVID-19 vaccines have been approved for use, Pfizer BioNTech (BNT162b2) and Moderna Spikevax (mRNA-1273), and as of March 20, 2022, more than 52 million doses of Pfizer and 22 million doses of Moderna have been administered in Canada, where this study was conducted. Clinical trials have demonstrated the vaccines are safe and monitoring of vaccinated people has shown side effects are mild and go away on their own. However, some rare, but serious, side effects have been observed after both vaccines, mainly myocarditis (inflammation of the heart).

While there have been many studies on either vaccine, few studies have been conducted to directly compare the safety of the two mRNA vaccines. Researchers in this study sought to compare the risk of myocarditis, pericarditis and myopericarditis between the Pfizer and Moderna COVID-19 vaccines.

People in the study were 18 years old or older and had received two primary doses of either Pfizer or Moderna vaccine in British Columbia, Canada, with the second dose between Jan. 1, 2021 and Sept. 9, 2021. Individuals whose first or second shot were administered outside of British Columbia or had a history of myocarditis or pericarditis within one year prior to second dose were excluded.

In all, more than 2.2 million second Pfizer doses were given and more than 870,000 Moderna doses. Within 21 days of the second dose, there were a total of 59 myocarditis cases (21 Pfizer and 31 Moderna) and 41 pericarditis cases (21 Pfizer and 20 Moderna). Researchers also looked at rates per million doses and the rate was 35.6 cases per million for Moderna and 12.6 per million for Pfizer-;an almost threefold increase after Moderna shots vs. Pfizer. Comparatively, rates of myocarditis in the general population in 2018, were 2.01 per million in people under age 40 and 2.2 per million in people over age 40.

Rates of myocarditis and pericarditis were higher with the Moderna vaccine in both males and females between ages 18 and 39, with the highest per million rates in males ages 18-29 after a second dose of Moderna.

According to the authors, the findings support recommending certain populations receive certain vaccines to maximize benefits and minimize adverse events.

Few population-based analyses have been conducted to directly compare the safety of the two mRNA COVID-19 vaccines, which differ in important ways that could impact safety. Our findings have implications for strategizing the rollout of mRNA vaccines, which should also consider the self-limiting and mild nature of most myocarditis events, benefits provided by vaccination, higher effectiveness of the Moderna vaccine against infection and hospitalization [found in prior studies], and the apparent higher risk of myocarditis following COVID-19 infection than with mRNA vaccination."

Naveed Janjua, MBBS, DrPH, lead author of the study and epidemiologist and the executive director of Data and Analytic Services at the British Columbia Centre for Disease Control

Limitations of the study include that it was observational, which limits the ability to determine causality between vaccination and myocarditis or pericarditis. However, temporality was ensured in the study design to limit the time studied between vaccine dose and myocarditis/pericarditis diagnosis. Also, the study relied on hospital and emergency department visit data and may have missed some less severe cases.

In a related editorial comment, Guy Witberg, MD, MPH, a cardiologist at Rabin Medical Center in Petah-Tikva, Israel, wrote the study is reassuring for vaccine safety since it provides further data that myocarditis is a very rare adverse event after both vaccines, and it is an important step toward a personalized approach to administering COVID-19 vaccines.

"[The study] should help put to rest 'vaccine hesitancy' due to concerns over cardiac adverse events," Witberg said. "This is one of only a few direct comparisons of the two widely adopted mRNA vaccines, and its results have practical policy implications: for a substantial segment of the population suffering from cardiovascular disease…these data give a strong argument to preferentially use the BNT162b2 [Pfizer] vaccine over mRNA-1273 [Moderna]."


  1. José Lázaro Da Silva Tradutor José Lázaro Da Silva Tradutor Brazil says:

    The article does not mention how many of those 30 or so per million that had a heart inflammation had serious discomfort or died.

  2. Captain Obvious Captain Obvious Australia says:

    The study also doesn't utilise a legitimate control whereby both injections are considered against non-injected individuals making the study practically useless for truly gauging safety. Additionally, while guaranteed to be excluded from the scope of any recent studies, why is that heart disease and circulatory issues have increased dramatically across the globe directly following the rollout of injection programs. Further why has there been an explosion around the globe of myocarditis for children under 14 post injection rollout; an age group not normally known for these types of issues. These junk studies need to be thrown into the same dumpster fire that all of the original Pfizer and Moderna "studies" have been fuelling for the past 2 years. The only thing attempting to be protected by these studies are the livelihoods and future incarceration status of health officials and the bank accounts of pharmaceutical companies.

  3. Cary Couture Cary Couture United Kingdom says:

    I've never died from catching a cold. I'll take my chances at completely avoiding myocarditis.

  4. AndiSho AndiSho Germany says:

    We can follow a complete proof chain.
    - spike IN heart muscle
    - autoantibodies
    - micro blood clots disable small capillaries to scarred tissue. In heart, kidney and blood-brain-barrier, they do not regenerate. This induces increasing capacity restriction, often sub-symptomatic for a long time. In crisis or under load, disaster strikes.

    It’s a SADS world.

    - NO persisting problem after infection of CoV (flu is something different), 1/2 yr later healed without scarring or persistent problems, ALL programs monitoring this have been stopped, contrary to some researcher from Basel stating “to be researched”…

    2,3-2,8% of vaccinees have elevated troponin and other heart parameters, show typical signs of myocarditis, and probably have a pre-damaged heart condition making them vulnerable life-long, as there IS NO MILD MYOCARDITIS.

    It is no “temporary” problem either.
    So ignore the words of soothing and take the numbers from Basel’s heart researcher.

    So they should treat this symptom “I once had a problem after vaccination” or even the fact alone “I’m vaccinated” as a commorbidity and compensate the risk by proper interventions. Especially if doing sports like biking in the mountains, or suffering from flu. ASAP stabilise against clotting. Black cumin oil, rupatadine or some heparin based therapy if physician has once advised it, ask for it again in times of crisis. In short: shoot away I-CARE as soon as having symptoms (forget the tests. And it works against flu as well;) or do I-RECOVER on a rather permanent basis.

    Until we find the real cures making symptoms unnecessary even after fading out the interventions. This is called healing.
    I think the Chinese found it a few thousand years ago, TCM energy build-up cure.
    And the Ayurveda Karma Cure.
    But the job is to teach this to each other. Teach it in regular schools!
    And to do these democratically, i.e. fulfil 5 conditions:
    cheap, available, safe and effective, and transparent, ie protected against structural corruption.

    Side note:
    - PEG alone re-programs the immune system “in an inheritable fashion”, i.e.: it kills the balance of our epigenetic programming, the Heritage of my Ancestors, the only thing that was left from them, 3-6 generations, depending on school of belief.
    Reducing nK, CD4, CD8, CD34+, from what I found so far...

    This also happens if pregnant women got vaccinated by skin contact etc., PEG also travels ANY barrier, also the placenta; or infants by eg breastmilk.
    (I’m not in favour of the theory it can be shed by aerosols.
    Before we overstrain aerosols, droplets and other hefty exchange of body fluids are more probably cause. ;)

The opinions expressed here are the views of the writer and do not necessarily reflect the views and opinions of News Medical.
Post a new comment

While we only use edited and approved content for Azthena answers, it may on occasions provide incorrect responses. Please confirm any data provided with the related suppliers or authors. We do not provide medical advice, if you search for medical information you must always consult a medical professional before acting on any information provided.

Your questions, but not your email details will be shared with OpenAI and retained for 30 days in accordance with their privacy principles.

Please do not ask questions that use sensitive or confidential information.

Read the full Terms & Conditions.

You might also like...
Study reveals a promising approach to developing universal influenza vaccine