Evaluation of Cardiac Troponin Levels in Individuals Aged 12-30 Years Following mRNA-1273 Vaccination: Results From a Randomized Placebo-Controlled Trial.

Background: Myocarditis is a very rare event following COVID-19 vaccination, with highest risk observed in males aged 12-24 years. Cardiac troponin I (cTnI) is a cardiac-specific biomarker of myocardial injury but is not etiologically specific and may be elevated in the absence of cardiac pathology, including after vigorous physical activity. This study assessed cTnI levels following administration of mRNA-1273.712 vaccine versus placebo in participants aged 12-30 years. Methods: In this phase 4, observer-blind, randomized, placebo-controlled, crossover study, participants received mRNA-1273.712 50 µg and placebo 28 days apart. Cardiac troponin I was measured at baseline and 3 and 28 days after injection. The primary endpoint was the proportion of participants with elevated cTnI 3 days after injection. Safety was monitored throughout. Results: Of the 1000 participants randomized, 981 had evaluable cTnI results; most (>98%) maintained normal cTnI levels at all measured time points, including at 3 days postinjection. 18/981 participants had ≥1 elevated cTnI result at any study time point; 7 of those 18 had elevations at baseline prior to any injection. Of the remaining 11 participants with normal baselines and no prior elevations, 3 had elevated cTnI 28 days after receiving mRNA-1273.712 and 8 had elevations after placebo. 11/18 participants with elevated cTnI reported recent physical activity, and none exhibited clinical signs or symptoms of myocarditis or pericarditis. No new safety concerns were identified. Conclusions: Cardiac troponin I elevations were low overall and were observed after both placebo and mRNA-1273 administration. Vaccination with mRNA-1273.712 in adolescents and young adults was not associated with elevated cTnI.