Myocarditis after RNA-based vaccines for coronavirus

Background: The incidence of myocarditis after RNA-based vaccines for coronavirus has gained social and medical interest.

Methods: We performed an intention-to-treat meta-analysis, following the PRISMA statement. After a systematic search, without language restriction, 9 publications were selected. Two were excluded (one was only in subjects with age 12-17 and other might had included subjects from a larger publication). We followed the PRISMA guidelines for abstracting data and assessing data quality and validity. Data was verified by 2 investigators.

Results: We analyzed 17,704,413 subjects, from 7 studies, that included 627 cases of confirmed myocarditis). The incidence of myocarditis was 0.0035% (95% CI 0.0034-0.0035). Mean incidence rate was 10.69 per 100.000 persons-year. Cases reported from Israel represented 45.14% from total (283 out of the 627). Only 1 case of fatal myocarditis or death was reported. There was significant heterogeneity between results. The meta-regression analysis excluded mean age, region, number of cases or number of people included as sources of heterogeneity. No small-study effect was observed (p = 0.19).

Conclusions and relevance: Myocarditis incidence after RNA vaccines is very rare (0.0035%) and has a very favorable clinical course.