COVID-19 vaccine induced myocarditis in young males: A systematic review

Abstract

Background: Myocarditis is a rare but significant adverse event associated with COVID-19 vaccination, especially for men under 40. If the risk of myocarditis is not stratified by pertinent risk factors, it may be diluted for high-risk and inflated for low-risk groups. We sought to assess how the risk of myocarditis is reported in the literature.

Methods: In accordance with PRISMA standards, we reviewed primary publications in PubMed, Embase, Google Scholar and MedRxiv (through 3/2022) and included studies that estimated the incidence of myocarditis/pericarditis after receiving either the BNT162b2 (Pfizer), mRNA-1273 (Moderna) or Ad26COVS1 (Janssen) vaccine. The main outcome was the percentage of studies using 4, 3, 2, 1 or 0 stratifiers (i.e. sex, age, dose number and manufacturer) when reporting the highest risk of myocarditis. Secondary outcomes included the incidence of myocarditis in males after dose 1 and 2 of the BNT162b2 (Pfizer) or mRNA-1273 (Moderna) vaccine.

Results: The 29 included studies originated in North America, Europe, Asia, or were Worldwide. Of them, 28% (8/29) used all four stratifiers, and 45% (13/29) used 1 or 0 stratifiers. The highest incidence of myocarditis ranged from 8.1-39 cases per 100,000 persons (or doses) in studies using four stratifiers. Six studies reported an incidence greater than 15 cases per 100,000 persons (or doses) in males aged 12-24 after dose 2 of an mRNA-based vaccine.

Conclusions: Only one in four articles reporting myocarditis used four stratifiers, and men younger than 40 receiving a second dose of an mRNA vaccine are at greatest risk.

Keywords: COVID-19 vaccination; epidemiology; health policy; myocarditis.

FIGURE 1

Highest myocarditis incidence from each study. Each bar represents a unique study. Data are grouped according to the number of stratifiers used. Stratifiers are sex, age, dose number and manufacturer. Each bar is labelled on the x‐axis with the stratifiers unique to the study that the estimate was obtained from. The number above each bar represents the myocarditis incidence. Male (M), Dose 2 (D2), Not Applicable (NA). In studies using four stratifiers, the stratifiers Male and Dose 2 were universally applicable

FIGURE 2

Myocarditis incidence in males after of BNT162b2 (Pfizer) vaccination. (A) Incidence of myocarditis after dose 1 of BNT162b2 vaccination. (B) Incidence of myocarditis after dose 2 (left) or after either dose 1 or 2 (right) of BNT162b2 vaccination. Sharff et al is an exception and combines data from Pfizer and Moderna vaccination. Estimates are grouped by the study they were collected from—indicated by the author listed on the x‐axis. Bars of the same colour are estimates from the same study but from a different age group. Incidence estimates were only included from studies that separated men from women and provided an estimate of the incidence of myocarditis in males after BNT162b2 vaccination

FIGURE 3

Myocarditis incidence estimates in males after mRNA‐1273 (Moderna) vaccination. (A) Incidence of myocarditis after dose 1 of mRNA‐1273 vaccination. (B) Incidence of myocarditis after dose 2 (left) or after either dose 1 or 2 (right) of mRNA‐1273 vaccination. Estimates are grouped by the study they were collected from—indicated by the author listed on the x‐axis. Bars of the same colour are estimates from the same study but from a different age group. Incidence estimates were only included from studies that separated males from females and provided an estimate of the incidence of myocarditis in men after mRNA‐1273 vaccination