Risk of Heart Inflammation in Children Elevated After Receiving Pfizer’s COVID-19 Vaccine: Study

A COVID-19 vaccine is prepared in a file image. Stephen Zenner/Getty Images

Children as young as 12 have an elevated risk of heart inflammation after receiving Pfizer’s COVID-19 vaccine, according to a new study.

Researchers with the U.S. Food and Drug Administration (FDA) and other institutions analyzed data from the FDA’s Biologics Effectiveness and Safety Initiative and looked for safety signals after Pfizer vaccination for children aged 5 to 17 between 2021 and mid-2022.

They found that myocarditis, a form of heart inflammation, and pericarditis, a related condition, met the threshold for a safety signal for children aged 12 to 17 after the second and third doses.

Safety signals don’t prove a vaccine caused an event, however, signals often trigger further research to attempt to prove causation.

Researchers sought to obtain medical records from the cases of myocarditis and pericarditis, and they obtained records for 37 of the 153 cases. Twenty-seven of those were confirmed as actual cases. Those children were hospitalized with a mean length of 2.8 days. Myocarditis or pericarditis set in within seven days for most of the patients.

Officials with the U.S. Centers for Disease Control and Prevention and researchers around the world say that the Pfizer and Moderna vaccines, both of which utilize messenger RNA (mRNA) technology, cause myocarditis and pericarditis.

The heart conditions can cause long-term problems and even death.

Researchers identified an elevated rate of myocarditis in the vaccinated in early 2021, and some countries have since paused or halted the administration of one or both of the mRNA shots to young people, especially young males. The United States hasn’t.

In the new study, researchers said they didn’t detect a signal for myocarditis or pericarditis for children aged 5 to 11. Other pre-specified outcomes, such as severe allergic shock, didn’t meet the signal threshold.

“The signal detected for myocarditis/pericarditis is consistent with published peer-reviewed publications demonstrating an elevated risk of myocarditis/pericarditis following mRNA vaccines, especially among younger males aged 12-29 years,” the researchers said.

They described myocarditis and pericarditis as a “rare event,” with an average incidence of 39.4 cases per million doses in children aged 5 to 17 within seven days after Pfizer vaccination. One of the citations was a CDC presentation (pdf). That presentation shows that, based on reports to the Vaccine Adverse Event Reporting System, the rate is as high as 75.9 in males aged 16 or 17 after the second dose of Pfizer’s vaccine.

Further, studies indicate the true rate is actually higher because adverse events from vaccines are underreported.

Pfizer’s vaccine is administered in a two-dose primary series. Booster doses are recommended for virtually all Americans older than 4 years old because the protection from the vaccines quickly wanes against newer virus variants.

Pfizer didn’t respond to a request for comment.

The study was published ahead of peer review on the medRxiv server.

Limitations of the new study, which was funded by the FDA, include the lack of stratification by sex.