The heart has played a central role in COVID-19 since its inception. Cardiovascular conditions are among the highest risk factors for hospitalization. A significant number of patients admitted with SARS-CoV-2 infections have signs of heart damage, and many recover from infection with permanent cardiovascular damage.
It is not surprising that debates about COVID-19 vaccines often revolve around issues involving cardiovascular health. The Danish football player Christian Eriksen's high-profile collapse in June set in motion a myth about the connection between sudden cardiac death and vaccination among athletes, which lasts for several months later.
Perhaps the most common point of conflict regarding COVID-19 vaccines is the risk of myocarditis after immunization, especially among adolescents.
What do the numbers tell us about COVID-19, vaccines and myocarditis?
What is myocarditis?
Myocarditis is an inflammation of the heart muscle that is most often caused by a virus such as the flu, coxsackie, hepatitis or herpes. Other causes include bacteria, fungi, toxins, chemotherapy and autoimmune conditions.
Some viruses infect the heart muscle and cause direct damage to the heart, while others cause heart damage indirectly through the immune system. Activation of the immune system in response to an infection triggers the release of chemicals in the body called cytokines, which help eliminate infections. In some cases, the level of cytokines rises to unusually high levels to produce a "cytokine storm" that causes damage to the heart muscle.
Myocarditis by the numbers
Prior to COVID-19, the incidence of myocarditis was between one and 10 cases per year. 100,000 people a year. The frequency is highest in men between 18 and 30 years. Interestingly, most cases of myocarditis are in the highest risk group in otherwise healthy and active people.
According to the US Centers for Disease Control and Prevention, the risk of myocarditis after infection with COVID-19 is much higher, with 146 cases per day. 100,000. The risk is higher for men, older adults (aged 50+) and children under 16 years. Footballer Alphonso Davies, 21, of Canada's men's national team, was put on the sidelines by heart inflammation after having COVID-19.
Myocarditis after COVID-19 vaccination is rare and the risk is much less than the risk of heart damage associated with COVID-19 itself.
Based on a study from Israel, the risk of post-vaccine myocarditis is 2.13 cases per 100,000 vaccinated, which is within the range normally seen in the general population. This study is consistent with others in the United States and Israel, which put the overall incidence of post-vaccine myocarditis between 0.3 and five cases per year. 100,000 people.
The children are well
The highest incidence of myocarditis after vaccination with mRNA vaccines has occurred within three to four days after the second vaccination in men under 30 years of age. In pediatric data, the median age is 15.8 years, with most patients being men (90.6 percent). and white (66.2 percent) or Hispanic (20.9 percent). Reliable booster shot data in this age group are not yet available.
Most studies show a clear benefit of COVID-19 mRNA vaccination with respect to myocarditis. Only one study conducted by Martina Patone of the University of Oxford and colleagues found more ambiguous results for individuals under the age of 40 based on myocarditis rates alone. However, considering the other adverse effects of SARS-CoV-2 infection - both cardiac and non-cardiac - there was still a strong benefit of immunizing younger people with COVID-19 vaccines other than Moderna, which research suggests has a higher risk of myocarditis than Pfizer's vaccine.
Repairing the damage
The treatment for myocarditis varies depending on its severity. Adults with mild myocarditis typically only need rest and non-steroidal anti-inflammatory drugs (NSAIDS) such as ibuprofen. More severe cases require medication or even mechanical circulatory supports such as left ventricular assist devices to support cardiac function. In some cases where the treatment is no longer effective, a heart transplant is required.
In a multicenter series of patients under the age of 21, those with mild symptoms received only NSAIDs or no anti-inflammatory treatment at all. Patients with more severe symptoms may receive stronger treatments, including intravenous immunoglobulin, glucocorticoids or colchicine in addition to NSAIDs.
How serious is it?
Over 80 percent of myocarditis cases unrelated to COVID-19 or COVID-19 vaccination disappear spontaneously, while five percent of patients die or must have a heart transplant within a year of diagnosis.
Adults who develop COVID-19 myocarditis have poorer outcomes than non-COVID-19 cases, including a higher risk of death. It should be noted that myocarditis associated with SARS-CoV-2 infection is merely one of several heart diseases associated with COVID-19 with outcomes that are worse than non-COVID-19 cases.
In the case of myocarditis after COVID-19 vaccination, the vast majority of cases are mild and disappear quickly. In adults, 95 percent of cases were considered mild. Similarly, in children, 98.6 percent are mild and there has been no reported need for mechanical cardiac support (extracorporeal membrane oxygenation when blood is pumped out of the body to a heart-lung machine) or death. All children who had heart weakness had complete normalization of their heart function at follow-up.
Message with home
The dynamic changes in the global pandemic, combined with the rapid development of research, make it challenging for the public to absorb all information about the risks and benefits of COVID-19 vaccines. In cases like this, it is helpful to seek the guidance of medical organizations whose mandate is to protect the health and well-being of society.
Given all the available research, organizations including the American Heart Association, the Canadian Cardiovascular Society, the Heart and Stroke Foundation of Canada, the Canadian Pediatric Society, and the American Academy of Pediatrics call on everyone who is eligible to be vaccinated against COVID-19.
It is a message we should all take to heart.
Do you have a question about COVID-19 vaccines? Send us an email at firstname.lastname@example.org and vaccine experts will answer questions in future articles.