In the study, researchers injected the mRNA vaccine into the
thigh muscles of mice via the standard intramuscular routes
and compared the outcomes with those of mice injected with
the intravenous route.
“We found that the heart of those mice receiving intravenous
vaccine developed obvious myocarditis and pericarditis
within 24 to 48 hours. This heart damage is greater even
after a second dose of vaccination 14 days later,” according
to the team.