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The remarkable development and rollout of Covid-19 vaccines will be hailed as a triumph of science. The rapidity of the process, though, opens the door to questions about side effects that could not have been detected in their clinical trials.

So far, unusual blood clots have been associated with administration of the AstraZeneca/Oxford and Johnson & Johnson vaccines, predominantly in younger women. More recently, reports have emerged that pericarditis (inflammation of the lining around the heart) and myocarditis (inflammation of the heart itself) have occurred, mainly in young men receiving mRNA-based vaccines. In this essay, we focus on myocarditis because, typically, it is a more serious condition than pericarditis (though severe cases of pericarditis can also be devastating).

Although most cases reported to date are mild and resolve without consequence, myocarditis can be a serious condition. It can cause severe declines in cardiac function; require hospitalization, artificial heart pumps, or even heart transplants; and may even be fatal.

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The Centers for Disease Control and Prevention issued guidance last week for patients and medical professionals about how to handle Covid-19 vaccinations in light of concerns about cardiac inflammation. The CDC frames the issue as a trade-off, something we agree with. The guidance describes the symptoms of myocarditis and the initial testing that might be used to confirm a diagnosis.

The guidance does not, however, advise against vaccination or even recommend that individuals who have experienced myocarditis — either from non-Covid-19 causes, from Covid-19 itself, or even from vaccination — discuss vaccination with their health care providers.

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Widely circulated slides from a recent meeting of the CDC’s Advisory Committee on Immunization Practices offered even more surprising recommendations. First, they recommended individuals receive “any FDA-authorized Covid-19 vaccine if heart has recovered” in those who have had myocarditis before vaccination. They also recommended pushing ahead with a second dose of an mRNA vaccine for individuals who developed myocarditis or pericarditis after a first dose if the heart has recovered “under certain circumstances,” even though a second dose could result in recurrent inflammation, which may be more severe than the initial bout and have lasting negative consequences on heart function.

We worry that this guidance does not give sufficient deference to the potential for recurrent myocarditis, and that anyone with a history of myocarditis or who develops myocarditis soon after Covid-19 vaccination should explore carefully with their health care providers about their options until the medical community better understands why this inflammation occurs and if it can be avoided through alternative approaches.

Indeed, the Food and Drug Administration fact sheets for health care providers administering both the Pfizer-BioNTech and the Moderna Covid-19 vaccines state that the decision to administer the vaccine “to an individual with a history of myocarditis or pericarditis should take into account the individual’s clinical circumstances.” But even here it would be better to recommend caution for routine administration of vaccines to those with a history of myocarditis before a discussion can take place between vaccine recipients and their health care providers. Even greater caution should be employed for administering these vaccines to individuals who experienced myocarditis after receiving a first dose. For now, among such individuals second doses should be considered only in those with high risk of exposure to SARS-CoV-2, the virus that causes Covid-19, or high risk of complications if they develop the disease.

There are precedent frameworks for considering complex trade-offs like this one. Some cancer medications (themselves wonders of modern medical science) can cause myocarditis and heart dysfunction, and so are used cautiously in those with a history of heart disease. Deciding to administer these drugs is not done lightly. In some cases, patients may be given additional rounds of these cancer drugs after the heart recovers from drug-induced heart complications if alternative treatments aren’t sufficient to treat their cancer. In such cases, however, the potentially large benefit to the individual often outweighs this risk. Even then, such decisions require careful discussion of risks and benefits.

If vaccine-induced myocarditis is indeed as uncommon as it seems, from a standpoint of population health there is no urgency to completing vaccination in this small group of individuals, since it will have no meaningful impact on when we achieve herd immunity. It could, however, have grave consequences for individuals who experience severe or recurrent myocarditis. And there are alternative options. Unless an individual is at very high risk for complications from Covid-19, a single dose of vaccine could provide adequate protection against serious, life-threatening illness without putting the individual at increased risk for vaccine-induced myocarditis (which has most often been described as occurring following the second dose). Some data suggest that the Moderna vaccine may be as much as 96% effective in teens after a single dose.

Individuals who have previously experienced myocarditis could also consider other options, such as delaying vaccination and continuing to social distance and wear a mask; or elect to receive a non-mRNA vaccine. Such decisions should be informed by personal preferences, risk of Covid-19 complications, likelihood of exposure to Covid-19, and evolving medical and scientific information.

Given the potential risks, individuals who have had myocarditis from any cause should have careful discussions with their physicians, and possibly with expert cardiologists, especially given safer alternatives. As practicing physicians in cardiology and hematology-oncology, we have received numerous questions about such concerns from family, friends, and patients. We admit that these are not easy choices, but the decision to simply proceed without deeper conversations seems insufficient.

Whether the number of vaccination-related cases of myocarditis could be further reduced by using smaller doses of the vaccine, more widely spaced doses, or a single dose is unclear at this time and patients with elevated risk of myocarditis should be made aware of these uncertainties as part of informed consent.

The Covid-19 vaccines are an undisputed triumph of modern medicine and science. We applaud efforts to increase uptake among those who are hesitant through confident, consistent, positive messaging. Yet as health care providers, we should not give the impression of minimizing serious complications like myocarditis in potentially at-risk individuals, as this may ultimately undermine this worthy goal.

Venkatesh L. Murthy is a cardiologist, professor of preventive cardiology, and associate professor of cardiology at the University of Michigan, Ann Arbor. Vinay Prasad is a hematologist-oncologist and associate professor of epidemiology and biostatistics at the University of California, San Francisco. Brahmajee K. Nallamothu is a cardiologist and professor of cardiology at the University of Michigan, Ann Arbor. Murthy reports owning stock in Eli Lilly, Pfizer, Johnson & Johnson, and Merck, which are marketing or developing products related to Covid-19. Nallamothu reports being a founder and shareholder of AngioInsight, a startup focused on improving the interpretation of coronary angiograms.

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