One in 35 health care workers at a Swiss hospital had signs of heart injury associated with the vaccine, mRNA-1273, researchers found.
"mRNA-1273 booster vaccination-associated elevation of markers of myocardial injury occurred in about one out of 35 persons (2.8%), a greater incidence than estimated in meta-analyses of hospitalized cases with myocarditis (estimated incidence 0.0035%) after the second vaccination," the researchers wrote in the paper, published by the European Journal of Heart Failure.
In a generally healthy population, the level would be about 1 percent, the researchers said.
The group experiencing the adverse effects was followed for only 30 days, and half still had unusually high levels of high-sensitivity cardiac troponin T, an indicator of subclinical heart damage, at follow-up.
The long-term implications of the study remain unclear as little research has tracked people over time with heart injury after messenger RNA vaccination, which is known to cause myocarditis and other forms of heart damage.
"According to current knowledge, the cardiac muscle can’t regenerate, or only to a very limited degree at best. So it’s possible that repeated booster vaccinations every year could cause moderate damage to the heart muscle cells," University Hospital Basel professor Christian Muller, a cardiologist and the lead researcher, said in a statement.
Moderna did not respond to a request for comment.
None of the patients experienced a major adverse cardiac event, such as heart failure, within 30 days of booster vaccination, and none had electrocardiogram changes.
The people with elevated levels were advised to avoid strenuous exercise, which may have mitigated more serious problems, the researchers said.
No imaging was done to examine the participants' hearts, despite imaging being recommended by many cardiologists in cases of suspected vaccine-induced myocarditis.
It's possible that imaging would have revealed inflammation, which could cause scarring or irregular heartbeat, Dr. Andrew Bostom, a heart expert in the United States who was not involved in the research, told The Epoch Times.
Study MethodsResearchers posited that the incidence of vaccine-associated heart injury was more prevalent than previously thought following messenger RNA booster vaccination because of a lack of symptoms or mild symptoms.
They defined injury as a sharp increase in high-sensitivity cardiac troponin T on the third day after vaccination without evidence of an alternative cause. The levels of cardiac troponin had to hit the upper limit of normal, 8.9 nanograms per liter in women and 15.5 nanograms per liter in men.
All workers at the University Hospital Basel scheduled to receive a Moderna booster for the first time were offered a chance to participate in the study, unless they experienced a cardiac event or underwent heart surgery within 30 days of vaccination. The workers received a booster, which is half the dosage level of the primary series shots, from Dec. 10, 2021, to Feb. 10, 2022. The cohort ended up being 777 workers, including 540 females. The median age was 37 years.
Among the participants, 40 had elevated levels of cardiac troponin. Alternative causes were identified in 18. For the other 22, the researchers determined they had "vaccine-associated myocardial injury." The median age of the 22 was 46. All but two were women, making the percentage of women with elevated levels higher than the percentage of men (3.7 percent versus 0.8 percent), which contrasts with most of the previous literature on vaccine-induced myocarditis. That could stem from women receiving a higher vaccine dose per body weight, the researchers said.
Baseline levels were not recorded because the hospital's COVID-19 task force and the researchers decided that the study "should interfere as little as possible with the motivation of the hospital staff to obtain the mRNA-1273 first booster vaccination and the logistics of booster vaccination itself."
None of the people with elevated markers had a history of heart disease. While half experienced symptoms, most symptoms were nonspecific like fever. Two participants suffered from chest pain. And two, according to the Brighton Collaboration case definition, likely suffered myocarditis.
Testing was done for high-sensitivity cardiac troponin T because of its sensitivity.
"This marker is extremely sensitive—with other methods such as MRI we wouldn’t have been able to detect any damage to the cardiac muscle, as it only becomes visible once the damage there is about three to five times greater," Dr. Muller said.
The researchers were not able to figure out the mechanism for the vaccine hurting the heart muscle.
The authors reported some conflicts of interest, including Dr. Muller reporting grants from drugmakers such as Novartis and Roche. The study was funded by the University of Basel and the University Hospital Basel.
Previous Findings, and Pending StudySeveral other prospective studies examine myocarditis following Pfizer vaccination.
The Swiss researchers said more prospective studies are needed to examine post-vaccination heart injury. Long-term problems from the injuries, they stressed, remain unclear.
Moderna was required by U.S. authorities to conduct a prospective study to assess the incidence of subclinical myocarditis following a booster among adults, with a projected completion date of June 30, 2023. Neither the U.S. Food and Drug Administration (FDA) nor Moderna have disclosed the results of the study as of yet.