Pfizer Vax Linked to FIRST EVER Right Ventricular Thrombus in 16-Year-Old After Third Shot

Monday, 11 August 2025

@THEWATCHTOWERS.ORG Staff reporting on a recently published case report in the journal Heart, Lung and Circulation (Volume 34, Supplement 4, S206, August 2025).

This post highlights the article’s description of a 16-year-old male who developed myo-pericarditis (inflammation of the heart muscle and surrounding sac) three days after receiving his third dose of the Pfizer-BioNTech COVID-19 mRNA vaccine. Five months later, the patient experienced recurrent chest pain, leading to the discovery of a 15×11 mm mobile, non-infective thrombus (blood clot) in the right ventricular outflow tract via echocardiography. This clot was surgically removed via re-do sternotomy, and the patient recovered uneventfully, being discharged on daily aspirin.Key Details from the Case Report:

• Patient Background: The adolescent had a prior history of ventricular septal defect repair but no other significant medical issues noted.
• Initial Presentation and Treatment: Symptoms of myo-pericarditis emerged shortly after the third vaccine dose, managed with colchicine for three months and ibuprofen for two weeks.
• Complication: The right ventricular thrombus was unprecedented in this context, not present on prior imaging. The authors suggest potential mechanisms like a pro-inflammatory response or molecular mimicry triggered by the vaccine, though the exact pathogenesis remains unclear.

Outcomes and Implications: The report emphasizes the rarity of such events but calls for vigilance in follow-up for patients with vaccine-induced myo-pericarditis, especially those with prior cardiac surgery. It raises questions about whether prophylactic antiplatelet or anticoagulant therapy might be warranted in similar cases, even if they don’t meet current guidelines, and stresses the need for further research into mechanisms and risk factors.

Right Ventricular Thrombus as a Possible
Complication of mRNA Vaccine-Induced MyoPericarditis: A Case Report

Case report (source)

The patient developed myo-pericarditis 3 days after receiving the third dose of the Pfizer COVID-19 vaccine. Initial management included colchicine for 3 months and ibuprofen for 2 weeks. Five (5) months later, the patient presented with recurrent chest pain, and transthoracic echocardiography (TTE) revealed a 15×11 mm mobile echogenic mass in the right ventricular outflow tract, suspected to be a thrombus (Figure). This mass was not present on earlier imaging. He underwent a re-do sternotomy, and the mass, identified as a non-infective thrombus, was resected. Postoperative recovery was uneventful, and he was discharged on daily aspirin therapy.