COVID-19 vaccine should wait to get their second dose.The National Advisory Committee on Immunization (NACI) updated its recommendations Friday, saying that individuals who experienced myocarditis and/or pericarditis after a first dose of mRNA vaccine should “wait to get their second dose until more information is available.” Myocarditis: What we know about the heart reaction reported after COVID-19 vaccines Myocarditis is the inflammation of the heart muscle, while pericarditis is the inflammation of the lining around the heart.There have been 65 cases of myocarditis/pericarditis as of June 18 in Canada out of 31.4 million vaccines administered at the time, according to federal government data.Out of the 65 cases, 50 had the.