Pfizer examined possible ways its COVID-19 vaccine causes heart inflammation, a newly disclosed document shows.
The company in a 2022 white paper acknowledged that its vaccine, BNT162b2, may be causing myocarditis, or heart inflammation, and a related condition called pericarditis.
Pfizer scientists claimed that the inflammation was likely not the result of direct cardiotoxicity, but did not rule out several other possible mechanisms, including that it stemmed from immune activity.
The immune system may be triggered by lipid nanoparticles, which in the messenger RNA (mRNA) shot deliver the spike protein, the document says.
“Although the BNT162b2 mRNA vaccine is optimized to reduce its detection by the innate immune system through the addition of nucleoside modifications and minimizing double-strand RNA impurity, it is possible, especially in certain individuals with genetic predisposition and underlying conditions that the immune responses to mRNA may not be sufficiently turned down and drive the activation of an innate and adaptive immune response,” they wrote in the 48-page white paper.
“This may lead to the excessive activation of proinflammatory cascades which contribute to the development of myocarditis,” they added.
Myocarditis is a serious condition that can be deadly for some people. Many occurrences after COVID-19 vaccination have been in healthy, young people. Young males are particularly at risk. The incidence is as high as 78.7 per million second doses in males aged 16 or 17, according to reports to the Vaccine Adverse Event Reporting System, with several dozen cases being reported after the second dose among males aged 12 to 15 and aged 18 to 24.
Myocarditis is also an issue after booster vaccination, data from the United States and other countries show.
The U.S. Centers for Disease Control and Prevention (CDC) is among the entities that have said the evidence shows the Pfizer and Moderna COVID-19 vaccines cause myocarditis.
