Myocarditis Higher With Moderna COVID Vax, but Overall Risk Low

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A new study shows a two- to threefold higher incidence of myocarditis/pericarditis following the second dose of the Moderna Spikevax mRNA-1273 COVID-19 vaccine compared with the Pfizer BioNTech BNT162b2 vaccine.

However, the overall rates of myocarditis/pericarditis remain ‘very low’ for both vaccines, supporting their favorable safety profile, the researchers emphasize.

The study was published online November 7 in the Journal of the American College of Cardiology.

Confirmed: Young Men at Highest Risk

Naveed Janjua, MBBS, PhD, with the British Columbia Center for Disease Control, Vancouver, Canada, and colleagues used data from the British Columbia COVID-19 cohort to compare the incidence of myocarditis, pericarditis, and myopericarditis following primary vaccination with the Pfizer BioNTech or Moderna mRNA vaccine.

The cohort included more than 2.2 million adults who received the Pfizer vaccine and about 871,000 who received the Moderna vaccine. Within 21 days of the second dose, there were 59 myocarditis cases (28 Pfizer and 31 Moderna) and 41 pericarditis cases (21 Pfizer and 20 Moderna).

Compared with the Pfizer vaccine, the Moderna vaccine was associated with more than twofold higher odds of myocarditis (adjusted OR [aOR]: 2.78; 95% CI, 1.67 – 4.62), pericarditis (aOR: 2.42; 95% CI, 1.31 – 4.46), and myopericarditis (aOR: 2.63; 95% CI, 1.76 – 3.93).

The overall rate of myocarditis/pericarditis per 1 million second doses was very low for both vaccine products but was higher for the Moderna vaccine than for the Pfizer vaccine (myocarditis: 35.6 vs 12.6; pericarditis: 22.9 and 9.4, respectively).

The association between the Moderna vaccine and myocarditis was stronger in men (aOR: 3.2; 95% CI, 1.77 – 5.83) and those younger than age 40 years (aOR: 5.09; 95% CI, 2.68 – 9.66) but was not present in people aged 40+ or women.

The population at highest risk for myocarditis after the second dose of Moderna vaccine is men younger than age 30 (269.6 cases per 1 million doses vs 58.1 with Pfizer), the researchers report.

They say their findings add to phase 3 clinical trial data and support findings from other passive surveillance systems that have observed an association between mRNA vaccine products and myocarditis/pericarditis. However, most prior analyses on this topic assessed the safety of mRNA vaccines separately and with no direct comparison, they point out.

In a news release, Janjua says the 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, and the apparent higher risk of myocarditis following COVID-19 infection than with mRNA vaccination.”

The researchers say further studies are needed to assess the risks of myocarditis/pericarditis with booster doses and lower-dose formulations of the Moderna vaccine.

Personalized Approach to Vaccination ?

The co-authors of a linked editorial say this analysis, combined with previous ones, continues to show that mRNA vaccine-associated myocarditis is a “very rare” event — one that is generally mild and associated with low morbidity and mortality and imaging findings suggestive of a benign long-term course.

Taken together, the data are “reassuring in terms of vaccine safety and should help put to rest ‘vaccine hesitancy’ caused by concerns over cardiac adverse events,” write Guy Witberg, MD, and Ilan Richter, MD, with the Cardiology Department, Rabin Medical Center, Petah-Tikva, Israel.

“Such a conclusion leans not only on the proven efficacy of the vaccines, but also on data showing that COVID-19 infection is associated with a much higher risk for myocarditis,” they add.

However, Witberg and Richter think the study also represents “an important step toward this personalized and tailored approach to vaccination.”

For adults with cardiovascular disease, especially those with left ventricular dysfunction, in whom minimizing the risk of myocardial insult is crucial, these data provide a “strong argument” to preferentially use Pfizer vaccine over the Moderna vaccine, they write.

Conversely, in the general population, particularly in people over age 40 and in women, the findings “support the equipoise between the 2 vaccines in terms of cardiovascular risks, allowing for health authorities to choose vaccine products according to factors such as cost and availability, which should improve resource utilization,” they add.

This work was supported by the British Columbia Cent er for Disease Control and the Canadian Immunization Research Network (CIRN) through a grant from the Public Health Agency of Canada and the Canadian Institutes of Health Research. This project was also supported by funding from the Public Health Agency of Canada through the Vaccine Surveillance Reference Group and the COVID-19 Immunity Task Force.  Janjua has participated in advisory boards and has spoken for AbbVie, not related to the current work. Witberg and Richter report no relevant financial relationships.

J Am Coll Cardiol. Published online November 7, 2022. Abstract, Editorial

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