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.

Importance: Twitter is used by health professionals to relay information. We sought to investigate the use of tweets to describe Mpox risks to children and young people in school during summer/ fall of 2022. Objective: To determine the number of tweets discussing the risk of Mpox to children and young people in school and 1) determine accuracy, 2) for inaccurate tweets, determine if risk was minimized or exaggerated and 3) describe the characteristics of the accounts and tweets which contained accurate vs. inaccurate information. Design: Retrospective observational study. Setting: Twitter advanced search in January 2023 of tweets spanning May 18th, 2022, to September 19th, 2022. Participants: Accounts labeled as: MD, DO, nurse, pharmacist, physical therapist, other health care provider, PhD, MPH, other Ed. degree, JD, health/medicine/public policy reporter (including students or candidates) who tweeted about the risk of Mpox to children and young people in school. Exposures: Tweets containing the keywords 'school' and 'mpox', 'pox', or 'monkeypox' from May to October 2022. Measures: The primary outcome was the total of and ratio of accurate vs inaccurate tweets, the latter further subdivided by exaggerating or minimizing risk, and stratified by account author credential type. Secondary outcomes included total likes, retweets and follower counts by accurate vs inaccurate tweets, by month and account credentials. Finally, Twitter user exposure to inaccurate vs accurate Mpox tweets was estimated. Results: 262 tweets were identified. 215/262 (82%) were inaccurate and 215/215 (100%) of these exaggerated risks. 47/262 (18%) tweets were accurate. There were 163 (87%) unique authors of inaccurate tweets and 25 (13%) of accurate tweets. Among health care professionals, 86% (95/111) of tweets were inaccurate. Only health reporters, (23/41) 56% of tweets, were more likely to provide accurate information, however this was driven by one reporter. Multiplying accuracy by followers and retweets, Twitter users were approximately 974x more likely to encounter inaccurate than accurate information. Conclusion: Credentialed Twitter users were 4.6 times more likely to tweet inaccurate than accurate messages. We also demonstrated how incorrect tweets can be quickly amplified by retweets and popular accounts. In the case of Mpox in children and young people, incorrect information exaggerated the risks 100% of the time.