Incidence Rates and Clinical Characteristics of Patients With Confirmed Myocarditis or Pericarditis Following COVID-19 mRNA Vaccination: Experience of the Veterans Health Administration Through 9 October 2022
Authors: Luo Jing , Hur Kwan , Salone Cedric , Huang Nina , Burk Muriel , Pandey Lucy , Thakkar Bharat , Donahue Mark , Cunningham Francesca 
Published: May 2023

Abstract

Background
Although the benefits outweigh the risks, COVID-19 vaccines have been associated with an increased risk of myocarditis and pericarditis. This report is based on a national US veteran population with confirmed myocarditis/pericarditis following mRNA COVID-19 vaccines according to the near real-time active surveillance program of Veterans Affairs.

Methods
This study is based on a cohort evaluation of all adults administered ≥1 mRNA COVID-19 vaccine, including boosters, in the Veterans Health Administration between 14 December 2020 and 9 October 2022. ICD-10-CM diagnosis codes were used to identify potential safety signals in near real time through a database analysis. All potential cases of myocarditis/pericarditis identified in the database analysis underwent in-depth chart review and case validation by a team of pharmacists and expert clinicians. Our main outcome was the incidence rate of confirmed myocarditis/pericarditis among vaccine recipients (overall and those aged 18–39 years) within 21 days of a first, second, or booster dose of a mRNA COVID-19 vaccine. We calculated the ratio of observed events among COVID-19 vaccine recipients over expected events from historical vaccine recipient controls (2015–2020) in the Veterans Health Administration. We used confirmed cases to calculate incidence rates and 95% CIs.

Results
Through 9 October 2022, 3 877 453 doses of BNT162b2 (Pfizer-BioNTech) and 4 221 397 doses of mRNA-1273 (Moderna) were administered as first or second dose across Veterans Affairs, and 1 012 561 BNT162b2 and 1 156 160 mRNA-1273 booster doses were administered. Among all doses, the rapid cycle analysis identified 178 potential cases of myocarditis/pericarditis among vaccinees of any age and 22 potential cases among those aged 18–39 years. Of these, 33 cases, including 6 among those 18–39 years old, were confirmed after in-depth chart review and validation, corresponding with an overall incidence rate per million ranging from 0.46 (95% CI, .01–2.55) for Moderna dose 1 to 6.91 (95% CI, 2.78–14.24) for Pfizer booster. Among those aged 18–39, incidence rates ranged from 7.1 (95% CI, .18–39.56) for Moderna dose 2 to 19.76 (95% CI, 5.38–50.58) for Pfizer dose 2. Patients with confirmed cases were hospitalized for a mean 4.1 days (range, 1–15). The final disposition for 32 (97%) of 33 cases was discharge to home.

Conclusions
This report is a real-world demonstration of the Veterans Affairs' active surveillance system for vaccines. Although the rapid cycle analysis initially identified 178 potential cases of myocarditis/pericarditis, only 1 of 5 cases was confirmed to be related to a COVID-19 vaccine after chart review. These findings highlight the paramount importance of active surveillance and chart validation for rare but serious adverse events related to COVID-19 vaccines.