Myocarditis, or heart inflammation, can be caused by the immune system after a viral infection. Symptoms of myocarditis include chest pain, shortness of breath and palpitations.

"Myocarditis is inflammation of the heart tissue. The most common time you get it is after a virus infection, but you can also get it after a heart attack," says cardiologist Daniel Anderson, MD, PhD. "We see it frequently after COVID-19 infection – up to 30% of patients show some evidence of myocarditis."

The background rate of myocarditis (meaning, how common it normally happens) is less than 2 in 10,000 people. So it's pretty rare. The Centers for Disease Control and Prevention is seeing a slightly higher rate in younger people after COVID-19 vaccination. "There's some evidence that suggests myocarditis is happening more than what you'd typically see," says Dr. Anderson.

Dr. Anderson has recently seen some myocarditis patients after COVID-19 vaccination. With treatment, they typically do very well.

What's causing this?

"We don't know why this is happening yet. However, we now are seeing more virus infections including rhinoviruses, echoviruses and non-COVID coronaviruses," says Dr. Anderson. "These viruses cause really common infections like the common cold. These colds are back now that people are not wearing masks or social distancing. My suspicion is that myocarditis after COVID-19 vaccination may be due to COVID-19 antibodies which are produced after the vaccine and that these antibodies might be interacting with another coronavirus infection that is by chance, overlapping with the vaccine.

"We have seen this occur in patients with a COVID-19 infection, and of interest, this occurs after a few weeks when the immune response is in full force and you are developing antibodies to the viral antigens of the COVID-19 infection. However, we simply are not sure what is happening yet."

What to watch for

The majority of myocarditis cases have occurred shortly after the second dose of Pfizer in young men. Myocarditis cases have been seen:

• Only after mRNA vaccines (Pfizer or Moderna)
• More commonly after the second dose
• Typically in people under 30 years of age

Take note of how your heart feels in the days after vaccination. If you experience chest pain, shortness of breath or palpitations, you need to see someone about such symptoms. If you have chest pain, call 911 or go to the emergency room.