![]() Lab tests among the myocarditis patients showed elevated levels of biomarkers of inflammation of the heart, heart damage, and systemic inflammation. Symptoms included chest pain, heart palpitations, fever, shortness of breath, sweating, headache, muscle pain, fatigue, and nausea. Most myocarditis patients began experiencing symptoms 1 to 4 days after the second dose of the Pfizer/BioNTech mRNA COVID-19 vaccine. No participants had evidence of previous SARS-CoV-2 infection. Most myocarditis patients (87%) were boys or young men (average age, 16.9 years) and were generally healthy before vaccination. Yale University researchers analyzed immune responses among 23 participants who developed post-vaccination myocarditis (generally mild, transient inflammation of the heart muscle) and healthy vaccinated control patients. The rare cases of myocarditis among recipients of mRNA COVID-19 vaccine-mostly in young men-are caused by a generalized immune-cell and inflammatory response rather than vaccine-triggered antibodies, suggests a small study published late last week in Science Immunology. "This study also found a low percentage of people reporting medical review or missing daily activities, suggesting that the vaccine is generally well-tolerated." "Absolute event rates were lower than in previous studies, which reported more than 30% systemic adverse events following both routes and local adverse event rates of more than 50% following subcutaneous administration and nearly 100% following intradermal vaccination," the authors said. For both routes, dose one produced more non-severe localized reactions, including redness, itching, and swelling. According to the authors, the adverse event rate was highest following dose one of intradermal vaccination (53%) and lowest following dose two of subcutaneous vaccination (31%). Vaccinations were classified as intradermal if administered in the forearm and subcutaneous if administered in the deltoid. This study also found a low percentage of people reporting medical review or missing daily activities. ![]() The participants received the vaccine from August 8, 2022, to March 20, 2023, and were asked about adverse events 0 to 7 days after the second dose. ![]() ![]() The median age was 41, and 97% of participants were men. The study was based on the results of a survey given to 13,306 participants. In late summer of 2022, Australia began to use the Jynneos vaccine with a dose-sparing schedule of 0.1-milliliter (mL) intradermal vaccine recommended for preexposure to mpox, and 0.5-mL subcutaneous vaccine for postexposure prophylaxis (prevention)-two doses given 4 weeks apart for both approaches. The study was published late last week in JAMA. An Australian postmarketing study of adverse events following Jynneos mpox vaccination finds that local adverse event rates were highest following intradermal administration, but absolute event rates were lower than in previous studies, and the vaccine was well tolerated overall. ![]()
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