COVID Vax Myocarditis Stays Mild With Good Prognosis Over a Year Later

People with postvaccine myocarditis did not share the typical mid-term complications associated with conventional myocarditis, based on a population-based study from France.

With 18-month follow-up of people who had been hospitalized for myocarditis during the COVID-19 pandemic, it appeared that composite clinical outcomes were more favorable if people had developed myocarditis soon after COVID-19 mRNA vaccination rather than conventional myocarditis (weighted HR 0.55, 95% CI 0.36-0.86).

Meanwhile, the risk of poor composite outcomes — counting hospital readmission for myopericarditis, other cardiovascular events, and all-cause death — was comparable between post-COVID-19 myocarditis and conventional myocarditis groups (weighted HR 1.04, 95% CI 0.70-1.52), according to Laura Semenzato, MSc, a statistician at Saint-Denis Cedex France in Paris, and colleagues.

These findings applied to young people and older myocarditis patients alike. “However, affected patients, mainly healthy young men, may require medical management up to several months after hospital discharge,” Semenzato’s group maintained in JAMA.

The authors added that their results, based on the French National Health Data System, are consistent with past data associating postvaccine myocarditis with a lower short-term risk of heart failure compared with other types of myocarditis.

“These data do confirm the largely favorable prognosis of patients with post-vaccine myocarditis. The extended follow-up provides additional reassuring evidence that while this is a real entity, very few patients suffer long term clinical consequences from this,” commented James de Lemos, MD, cardiologist at UT Southwestern Medical Center in Dallas.

The results support the notion that “vaccine associated myocarditis is fundamentally different, and much lower risk, than COVID myocarditis and non-COVID, non-vaccine myocarditis,” he told MedPage Today.

Indeed, although the preponderance of evidence points to a causal relationship between the first mRNA COVID-19 vaccines and myocarditis — occurring more often in young men and adolescent boys — postvaccine myocarditis has been rare and fairly mild. Reports show a few days of hospitalization being typical for recovery, and the fear of excess sudden cardiac deaths among affected people has yet to become reality.

“Given the effectiveness of vaccines, these facts point to the unmistakable conclusion that [coronavirus] vaccines remain a safe and crucial part of dealing with this now-endemic virus,” according to cardiologist James Januzzi Jr., MD, of Massachusetts General Hospital and Harvard Medical School, both in Boston.

Indeed, mainstream public health officials continue to endorse COVID vaccines for prevention among children and adults.

Last week, the FDA approved and granted emergency use authorization to the updated vaccines from Moderna (Spikevax) and Pfizer-BioNTech (Comirnaty) for people ages 6 months and older. These new vaccines target the KP.2 strain of SARS-CoV-2 to better target currently circulating variants.

CDC Director Mandy Cohen, MD, MPH, quickly endorsed giving these vaccines to every individual ages 6 months and older.

“I tell my patients on a routine basis they should be vaccinated when appropriate. Since a new variant is out there, rates of COVID are rising quite substantially. The good news is that a new version of the vaccine is now available, which is tailored for the current variant that is circulating,” Januzzi wrote in an email.

For their French cohort study, Semenzato’s group used a database that covered all individuals, ages 12-49 years, who were hospitalized for myocarditis between Dec. 27, 2020 and June 30, 2022.

These were 4,635 people included in total: 12% with postvaccine myocarditis (within 7 days after COVID-19 mRNA vaccine), 6% post-COVID-19 myocarditis (within 30 days of SARS-CoV-2 infection), and 82% conventional myocarditis (remainder of cases).

Patients with postvaccine myocarditis were younger and more frequently men compared with the other groups. Two-thirds of postvaccine myocarditis cases occurred after a second vaccine dose.

Trends in medical management of people after hospitalization were similar across the three myocarditis groups.

The authors noted that one patient with postvaccine myocarditis had required extracorporeal membrane oxygenation. After hospital discharge, the person died, and myocarditis was judged the most likely cause of death.

Semenzato and colleagues said 18-month follow-up was complete for 99% of the population.

Despite the large sample, they nevertheless cautioned that they were unable to capture cases of myocarditis that did not require hospitalization, and results may vary depending on how postvaccine myocarditis is defined.

One important question that remains unanswered in this field is why some people develop myocarditis after getting a COVID-19 mRNA vaccine and not others.

“The mechanisms producing myocardial injury after administration of a COVID-19 mRNA vaccine are not well understood, with various hypotheses such as an altered gene expression, direct immune activation by mRNA, molecular mimicry, immune dysregulation, or aberrant cytokine expression,” Semenzato and colleagues wrote.

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