Case ascertainment of myocarditis following COVID-19 booster vaccine

In a recent study posted to the medRxiv* preprint server, a team of researchers from the United States (US) performed a time case surveillance of myopericarditis following coronavirus disease 2019 (COVID-19) booster vaccination in a cohort of health plan members of Kaiser Permanente Northwest Health System, Portland, Oregan.

Study: Surveillance of Myopericarditis following COVID-19 Booster Dose Vaccination in a Large Integrated Health System. Image Credit: Lightspring/ShutterstockStudy: Surveillance of Myopericarditis following COVID-19 Booster Dose Vaccination in a Large Integrated Health System. Image Credit: Lightspring/Shutterstock

Myopericarditis involves the inflammation of muscles and the outer lining of the heart and, in severe cases, may cause heart failure and death. To date, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccination-induced risk of myopericarditis has not been investigated extensively. According to the authors, the Vaccine Safety Datalink (VSD) analysis detected lower adverse effects related to myopericarditis post-COVID-19 messenger ribonucleic acid (mRNA) vaccination.

However, this data omitted International Classification of Diseases (ICD-10) codes during retrieval of claims for hospital discharge, and there were delays of weeks in insurance claims from a community hospital. The current study was performed to provide a more timely and complete case assessment of myocarditis following COVID-19 booster dose vaccination.

Study design

In this current work, the researchers studied a cohort of 65,785 health plan members of Kaiser Permanente, Northwest, aged between 18 to 39 years who have been administered with a booster dose of COVID-19 vaccine and completed at least five months post-primary vaccination series.

The team identified the cases of myopericarditis or pericarditis by retrieving the health records of the National Center for Health Statistics (NCHS) for all outpatients and inpatients encountered through January 18, 2022, using diagnosis codes of ‘myocarditis’ or ‘pericarditis’ as a text label. The cohort was analyzed for 21 days post booster SARS-CoV-2 vaccine administration. Any member with a previous history of myocarditis or pericarditis before the first vaccination dose of COVID-19 was excluded from the study. Identified patients records were independently reviewed and classified into confirmed, probable, or excluded based on the surveillance case definition of Centers for Disease Control and Prevention (CDC) for myocarditis and pericarditis by two physicians.


The team identified six patients, among 65,785 members who have been inoculated with a booster dose of SARS-CoV-2 vaccination and met the criteria for acute myocarditis or pericarditis as per CDC within 21 days of infection. Among the six cases of myocarditis, four cases were reported in a population of 27,253 men. All the identified six cases received a booster dose of Pfizer vaccine.

The team noted that out of six patients, five patients reported chest pain within four days of vaccination, although one patient developed chest pain after eight days. Patient number 6 showed the symptoms of pain in the chest, myocarditis, and cardiogenic shock after administering the booster dose. Patient number 5, who received a heterologous series of Johnson and Johnson SARS-CoV-2 vaccine as a primary dose and Pfizer vaccine as a booster dose, developed mild myocarditis.

Overall, the researchers observed that for every 100,000 COVID-19 booster doses administered, 9.1 cases of myopericarditis were detected (95% CI 3.4 to 19.9). For every 100,000 booster doses administered in men, 14.7 cases of myopericarditis (95% CI 4.0 to 37.6) were observed.


The findings of this study estimated more than nine cases of myopericarditis incidents per 100,000 COVID-19 booster doses which are higher than the prior estimates provided by the Vaccine Adverse Event Reporting System (VAERS).

This shows that the current surveillance system may underreport incidents of myopericarditis following COVID-19 booster vaccination. So the consideration of case estimates provided in this study is essential while modeling risk and benefits for implementing the wide-scale vaccination program and further sequential development of the future COVID-19 vaccines for the general public.

*Important notice

medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

Journal reference:
Sangeeta Paul

Written by

Sangeeta Paul

Sangeeta Paul is a researcher and medical writer based in Gurugram, India. Her academic background is in Pharmacy; she has a Bachelor’s in Pharmacy, a Master’s in Pharmacy (Pharmacology), and Ph.D. in Pharmacology from Banasthali Vidyapith, Rajasthan, India. She also holds a post-graduate diploma in Drug regulatory affairs from Jamia Hamdard, New Delhi, and a post-graduate diploma in Intellectual Property Rights, IGNOU, India.


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