Temporal relationship of myocarditis and pericarditis following COVID-19 vaccination: A pragmatic approach.

Background: Complications following COVID-19 vaccination, particularly with mRNA vaccines, rarely include myocarditis and pericarditis. This work principally aimed at defining a realistic temporal relationship between vaccination and myocarditis/pericarditis development.

Methods: All relevant cases reported from week 52/2020 through week 41/2021 in the VAERS database were retrieved and analyzed for licensed vaccines. These included BNT162b2, mRNA-1273, and AD26.COV2·S. Incidence rates were calculated using the corresponding administered vaccine doses as denominators. Additionally, analyzed parameters included demographics, dose series, hospitalization length and outcome.

Results: Overall, 2016 myocarditis and 1380 pericarditis cases, (4.96/10 and 3.40/10 administered vaccine doses, respectively), were recorded. Most myocarditis cases occurred following BNT162b2 (5.60/10 doses) in males <30 years. Pericarditis affected predominantly males <40, both sexes >40 years, and was most common post AD26.COV2·S (4.78/10 doses). Hospitalization was required for 40.3% and 27.2% of myocarditis and pericarditis cases, respectively. A bimodal pattern was found for both myocarditis and pericarditis, with two peaks that coincided temporally, but were reversed in intensity. The first peak was recorded 1-3 days post-vaccination and was more pronounced in myocarditis, while the second was recorded 15-30 days post-vaccination and was more intense in pericarditis.

Conclusions: Myocarditis/pericarditis after COVID-19 vaccination is rare and depicts a bimodal pattern.