US CDC: Heart Inflammation Following Pfizer BioNTech and Moderna mRNA COVID-19 Vaccination

Written by Dr. K. on June 11th, 2021.

According to the US Centers for Disease Control and Prevention (CDC), there have been increased reports to the Vaccine Adverse Event Reporting System (VAERS) of cases of inflammation of the heart, called myocarditis and pericarditis, happening after mRNA COVID-19 vaccination (Pfizer-BioNTech and Moderna) in the United States since April 2021.

According to data from two vaccination safety monitoring systems, a higher-than-expected number of young men developed cardiac inflammation following their second dosage of the mRNA Covid-19 injections from Pfizer/BioNTech and Moderna, according to the US Centers for Disease Control and Prevention (CDC).

Myocarditis refers to inflammation of the heart muscle, whereas pericarditis refers to inflammation of the heart’s outer lining. In both circumstances, the immune system responds to an infection or another trigger by inducing inflammation.

These reports are rare, given the number of vaccine doses administered, and have been reported after mRNA COVID-19 vaccination (Pfizer-BioNTech and Moderna), particularly in adolescents and young adults, the CDC added.

The CDC and other health regulators have begun investigations into these heart inflammation cases after Israel's Health Ministry stated that it had discovered a possible relationship to the condition in young men who received Pfizer's Covid-19 vaccination.

There has not yet been a proven causal relationship between covid vaccinations and cases of myocarditis or pericarditis, however this is still being investigated, according to the agency. The CDC added that “whilst some patients required hospitalisation, most have fully recovered from their symptoms”.

According to the cases reported to VAERS, most of the recorded cases occurred in male adolescents and young adults ages 16 years old or older. These were more often after getting the second dose of either Pfizer-BioNTech or Moderna, with symptoms typically presenting several days after COVID-19 vaccination.

“We clearly have an imbalance there," Dr. Tom Shimabukuro, deputy director of the Centers for Disease Control and Prevention’s Immunization Safety Office, said during a meeting of the US Food and Drug Administration’s Advisory Committee on Thursday.

Dr Shimabukuro added that “the overwhelming majority of the cases have occurred within a week of vaccination. There is also a predominance of males in younger age groups among the reported heart inflammation cases.” Dr Shimabukuro said the US data is consistent with findings from Israel’s vaccinated population.

On Thursday, the CDC said it had identified a total of 216 cases of heart inflammation after an initial dose of an mRNA vaccine and another 573 cases after the second shot.

To date, about 130 million Americans have received both doses of one of the two mRNA vaccinations that are now authorized. The Pfizer-BioNTech vaccine, which was authorised for adolescents 12 and older on 10th May 2021, has already been administered to a large number of teenagers.

Pfizer said it agrees with the CDC's assessment of the cases of heart inflammation, adding that “the number of reports is small given the number of doses administered.” “It is important to understand that a careful assessment of the reports is ongoing and it has not been concluded that the mRNA Covid-19 vaccines cause myocarditis or pericarditis," Pfizer said in a statement.

Moderna further stated that no causal link between the condition and the vaccine has been identified. It said that it is actively working with public health and regulatory agencies to better assess the issues.

Given the risk of COVID-19 illness and related, potentially severe complications such as long-term health complications, hospitalisation, and even death, the CDC continues to recommend COVID-19 vaccination for everyone 12 years of age and older. “It’s vital to obtain the second dose of the Pfizer-BioNTech or Moderna vaccine unless a vaccination provider or your doctor advises you not to," the CDC noted.

COVID-19 vaccination offers documented and established advantages that outweigh the risks, which include the risk of myocarditis or pericarditis. In addition, most patients with myocarditis and pericarditis who received treatment responded well to medications and rest, and felt much better quickly.

The Advisory Committee on Immunization Practices of the Centers for Disease Control and Prevention will meet on June 18th 2021 to evaluate an increase in reported cases of the condition, especially among teenagers and young adults. Pfizer-BioNTech and Moderna use mRNA technology in their covid vaccines.



  1. CDC
  2. Bloomberg News
  3. Reuters
  4. Malaysia Kini

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