The new information comes from the Centers for Disease Control and Prevention’s National Patient-Centered Clinical Research Network (PCORnet) and from a separate large international clinical study published online in Circulation.
CDC data
The CDC study analyzed electronic health record data from 40 U.S. health care systems from Jan. 1, 2021, to Jan. 31, 2022, on more than 15 million people aged 5 years or older.
It reports a rate of myocarditis or pericarditis after mRNA COVID-19 vaccination of 0-35.9 per 100,000 for males and 0-10.9 per 100,000 for females across different age groups and vaccine cohorts.
Rates of myocarditis or pericarditis after SARS-CoV-2 infection ranged from 12.6 to 114 per 100,000 for males and from 5.4 to 61.7 per 100,000 for females across different age groups.
Even among males aged 12-17 years, the group with the highest incidence of cardiac complications after receipt of a second mRNA COVID-19 vaccine dose, the risk was 1.8-5.6 times higher after SARS-CoV-2 infection than after vaccination, the CDC report notes.
“These findings provide important context for balancing risks and benefits of mRNA COVID-19 vaccination among eligible persons greater than or equal to 5 years,” the report states. They also “support the continued use of recommended mRNA vaccines among all eligible persons aged greater than or equal to 5 years,” it concludes.
International study
The international study focused on prevalence, clinical characteristics, and outcomes of clinically manifest acute myocarditis in patients with COVID-19 infection.
The study showed a rate of acute myocarditis of 2.4 per 1,000 patients hospitalized with COVID-19.
“A small study previously indicated acute myocarditis is a rare occurrence in people infected with COVID-19. Our analysis of international data offers better insight to the occurrence of acute myocarditis during COVID-19 hospitalization, particularly before the COVID-19 vaccines were widely available,” coauthor Enrico Ammirati, MD, PhD, Niguarda Hospital, Milan, commented.
“This analysis indicates that, although rare, hospitalized patients with acute myocarditis associated with COVID-19 infection have a much greater need for intensive care unit admission, in up to 70.5% of the cases, despite the average age of the individuals in the study being much younger than expected, at 38 years old,” added coauthor Marco Metra, MD, University of Brescia, Italy.
The researchers report that the use of corticosteroids in patients with acute myocarditis appeared safe, and, in most cases, a rapid increase in the left ventricular ejection fraction was observed. In addition, they say that discharged patients with acute myocarditis had “an excellent short-term prognosis without occurrence of cardiovascular events.”
The authors also point out that these data show much higher frequency and severity of acute myocarditis linked to COVID-19 infection, compared with myocarditis cases linked to the mRNA COVID-19 vaccines.
The international study examined health data on 56,963 patients who were hospitalized with COVID-19 at 23 hospitals across the United States and Europe from February 2020 through April 2021.
Among these patients, 97 with possible acute myocarditis were identified (4.1 per 1,000), of whom 54 (2.4 per 1,000) were classified as having “definite or probable” acute myocarditis supported by endomyocardial biopsy (31.5% of cases) or magnetic resonance imaging (92.6% of cases).
The median age of definite/probable acute myocarditis cases was 38 years, and 39% were female. On admission, chest pain and dyspnea were the most frequent symptoms (55.5% and 53.7%, respectively), and 31 cases (57.4%) occurred in the absence of COVID-19–associated pneumonia. A fulminant presentation requiring inotropic support or temporary mechanical circulatory support occurred in 21 cases (39%).
Overall, 38 patients (70.4%) were admitted to the intensive care unit for a median time of 6 days. Ten patients (18.5%) received temporary mechanical circulatory support for a median time of 5 days. Three patients died (5.5%) during the index hospitalization, all of whom also had pneumonia. At 120 days, estimated mortality was 6.6%. Patients with pneumonia were more likely to develop hemodynamic instability, require mechanical circulatory support, and die, compared with those without pneumonia.
The authors note that their reported prevalence of acute myocarditis associated with COVID-19 is lower, compared with studies that performed universal cardiac MRI screening during the convalescent COVID-19 period.
They say that underestimation of the prevalence of mild or subclinical acute myocarditis is likely in this study because of the retrospective nature of the registry, the lack of systematic cardiac MRI, and the possibility of missing some diagnoses, particularly during the first pandemic wave when cardiac MRI and endomyocardial biopsy were less frequently performed.
The authors also point out that data on myocarditis after COVID-19 vaccination suggest that vaccination-linked myocarditis is milder than that associated with the virus itself.
With regard to the prevalence of acute myocarditis after vaccination, they report that among 2.8 million doses of mRNA COVID-19 vaccine in the armed forces, 23 individuals had evidence of acute myocarditis, suggesting a prevalence of less than 1 case of acute myocarditis per 100,000 mRNA COVID-19 vaccine doses.
They note that the CDC has also reported 399 reports of myocarditis among 129 million fully vaccinated individuals with the mRNA COVID-19 vaccines.
“These figures appear reassuring, compared with the prevalence of clinically manifest acute myocarditis observed in this study among hospitalized patients with COVID-19,” they conclude.
A version of this article first appeared on Medscape.com.