Thread by @a_husby

A rare side-effect of SARS-CoV-2 mRNA vaccines is myocarditis. The prognosis of this side-effect is not well established.

Using information from 23+ mil. residents in four countries (🇩🇰,🇫🇮,🇳🇴,🇸🇪), we compared this kind of myocarditis to other types:
bmjmedicine.bmj.com/content/2/1/e0…
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The article with our findings: "Clinical outcomes of myocarditis after SARS-CoV-2 mRNA vaccination in four Nordic countries" has just been published (with open access) in BMJ Medicine (@BMJMedicine) and below I give a short 🧵, describing our findings...
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Building on previous collaborative studies, we used combined nationwide registry data from Denmark, Finland, Norway, and Sweden to follow 7,292 individuals who where admitted with new-onset myocarditis in 2018-2022 (see manuscript and supplement for nitty-gritty details).
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We categorized myocarditis patients as
- SARS-CoV-2 mRNA vaccine myocarditis,
- COVID-19 myocarditis, or
- Conventional myocarditis,
based on whether myocarditis occurred within 28 days of vaccination, covid-19, or neither.
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The individuals were followed up for 90 days for heart failure, death or readmission to hospital.
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Patients with vaccine myocarditis had a decreased relative risk of heart failure compared with conventional myocarditis.
The relative risk of death was 0.48 (0.21-1.09) for patients with vaccine myocarditis and 2.35 (1.06-5.19) for patients with covid-19 myocarditis.
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The patterns of association also were similar when using 10-day intervals.
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With regards to readmission, the estimated risk of readmission to hospital was numerically lower for patients with vaccine myocarditis compared with those with conventional myocarditis, and comparable to covid-19 myocarditis.
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In a subgroup analysis of myocarditis patients, we also investigated the risk of heart failure or death among younger individuals (age 12-39 years), without predisposing comorbidities.
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We found that vaccine myocarditis was associated with a non-significant reduced relative risk of heart failure or death compared with conventional myocarditis (relative risk 0.50, 95%CI 0.22-1.12).
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We also found that covid-19 myocarditis was associated with an increased risk of heart failure or death (relative risk 5.78, 95%CI 1.84-18.20) compared with vaccine myocarditis.
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For more details and discussion, read the paper at:
bmjmedicine.bmj.com/content/2/1/e0…
12/14

My deepest gratitude goes to my insightful co-authors Hanne Løvdal Gulseth, Petteri Hovi, @JorVinHan , Nicklas Pihlström, Nina Gunnes, @TommiHrknen , Jesper Dahl, @okarlstad , Tiina Heliö, Lars Køber, Rickard Ljung, and @anders_hviid
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Lastly, a big thanks goes to @SSI_AEF / @SSI_dk for hosting me during this project. I'm also grateful for BMJMedicine (@BMJMedicine) for guiding the peer-review process.
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