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  • A Canadian study shows that myocarditis and pericarditis after COVID-19 mRNA vaccinations are extremely rare.
  • This research also suggests that spacing out second doses to 30 days and offering Pfizer vaccines over Moderna might lower the risk of developing these conditions in men ages 12-29.
  • Experts stress that developing COVID-19 poses a greater risk of myocarditis and pericarditis than being vaccinated.

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Experts at the University of Alberta in Canada have analyzed evidence on the risk of myocarditis and pericarditis after COVID-19 vaccination and found the risk is low, including among young men. These conditions, typically caused by viral infections, involve inflammation of heart tissues.

The findings do confirm that the issues occur more frequently among young males shortly after a second dose of the mRNA vaccine.

Most cases have been mild, and the risk appears to be higher after receiving Moderna’s mRNA vaccine than Pfizer’s counterpart.

The researchers propose that using Pfizer over Moderna and spreading out dosing intervals might reduce risks for younger individuals.

This study appears in the BMJ.

Myocarditis refers to the inflammation of the heart muscle, and pericarditis occurs when there is inflammation of the sac surrounding the heart. Both conditions are typically caused by a viral infection.

The conditions are rare but serious. Fortunately, most people fully recover.

An uptick in cases after COVID-19 mRNA vaccinations has generated concern among medical and public health leaders.

Reports first appeared in April 2021, leading to monitoring side effects after vaccination with Pfizer and Moderna’s mRNA vaccines.

Pediatric and heart specialists at the University of Alberta analyzed over 8,000 cases after combing through 46 studies.

They started investigating records of people in every age group and zoned in on individuals 0-39 years of age. According to the researchers, incident rates in adults ages 40 years and older were “very low to none.”

How frequent are they?

The researchers noted that the overall rates of myocarditis are 1-2 cases per 100,000 person-years in the United States. Person-years is a measurement used in prospective studies where researchers consider the number of participants involved and how much time each person spends in the study. If a study followed 100 people for 20 years, the research would contain 2,000 person-years of data.

The study found that rates of myocarditis after COVID-19 vaccination are 0.2 per one million people — and 1.4 per one million for pericarditis.

They found that adolescent and young adult males had the highest incidences of myocarditis after receiving mRNA vaccines against SARS-CoV-2. The findings are in keeping with historical tendencies concerning this condition.

Male teens ages 12-17 years had 50-139 cases per million, and male adults ages 18-29 had 28-147 cases per million.

Moderna vs. Pfizer

Medical News Today discussed this study with Dr. Jorge Moreno, an assistant professor of medicine at the Yale School of Medicine. He was not involved in the study.

Dr. Moreno agreed that cases of COVID-19 vaccine-related myocarditis and pericarditis are rare.

He also stressed that “COVID, the illness, can also [cause] myocarditis, and that is much more likely than the vaccine itself [causing it].”

Dr. Moreno mentioned that some European nations prefer the Pfizer COVID-19 vaccine, which appears to carry a lower risk of myocarditis than the Moderna vaccine.

However, he added, “the FDA and the CDC here in the U.S. did not find that the difference was substantial enough to make that recommendation.”

Change dosing schedule?

The researchers also found that the risk of myocarditis or pericarditis may be lower if people receive their second vaccine dose more than 30 days after the first.

Data specific to young males suggests that increasing dosing intervals to over 56 days may significantly reduce rates of the conditions.

Dr. Moreno felt that more studies are needed to evaluate the idea of spacing vaccine doses.

Currently, the World Health Organization (WHO) does not recommend that people under 18 receive a booster shot.

The authors stressed that data for risk factors were limited. They hope that future studies will include tissue samples and long-term follow-up to “enhance understanding of mechanism[s]” driving the heart conditions.

The COVID-19 landscape is rapidly changing, calling for constantly evolving research.

In a linked editorial, some U.S. researchers pointed out that risks related to boosters and vaccinating young children remain unclear. The long-term outcomes of people who develop myocarditis are also yet to be understood.

MNT also spoke with Dr. Jeffrey J. Hsu, a cardiologist at UCLA Health, concerning the present study. He was not involved in the research.

Dr. Hsu said he is worried that myocarditis and pericarditis concerns may have deterred some people from getting vaccinated:

“While studies such as this one show that these conditions do occur rarely after vaccination, my concern is that the results of these studies are either misinterpreted or distorted when communicating them to the public.”

Dr. Hsu and Dr. Moreno emphasized that relaying information with empathy makes the most effective strategy for encouraging the vaccine-hesitant.

Dr. Hsu stated: “We have much more data on both the benefits and risks of vaccination now compared to earlier in the pandemic and it is important for clinicians to clearly communicate our latest understanding of the impact of vaccination. Also, for patients who are hesitant to proceed with vaccination, I have found it helpful to spend the time to understand their specific reservations.”

Cultural challenges

Dr. Moreno explained why some people remain unaware or skeptical of the effectiveness and safety of vaccines.

For instance, a considerable proportion of the Hispanic population faces a language barrier. The assistant professor added: “I think that there is a lot of mistrust in the healthcare system from years of issues that have come up, whether it’s getting access to healthcare [or] insurance issues.”

Dr. Moreno also said reaching many Hispanic and Black individuals require a deeper understanding of cultural differences.

Dr. Hsu commented: “For some people, it is clear that nothing will change their stance on vaccination, while others may just be seeking clearer information from a trusted source, such as their physician.”