SARS-CoV-2 vaccination and myositis in Norway and Sweden
Authors' conclusion
In this nationwide study of >13.6 million person-years in two countries, there were no signs of an increased risk of myositis after SARS-CoV-2 vaccination, neither after the mRNA vaccines nor after the adenoviral vector vaccine.
Study context
- Population
- Persons in Norway and Sweden who turned 12 years or older in 2021, resident on 27 December 2020; followed to 21 May 2023
- Participants
- 13 million persons>13.6 million person-years
- Exposure
- 180-day risk periods after messenger ribonucleic acid (mRNA) or adenoviral vector SARS-CoV-2 vaccine vs unvaccinated periods
- Outcome
- Incident myositis diagnosis
- Follow-up
- 180 days after each dose
Methodological detailsnationwide, Poisson regression, adjusted for sex, age, occupation (health-care worker), region, positive COVID-19 test and comorbidities
- Nationwide
- Poisson regression
- Adjusted for sex, age, occupation (health-care worker), region, positive COVID-19 test and comorbidities
Main finding
As reported in the abstract
Myositis · 180 days
mRNA
99
events
Adenoviral vector
13
events
Unvaccinated
101
events
Adjusted incidence rate ratio (95% CI)
mRNAvs Unvaccinated
0.84(0.63–1.11)
Adenoviral vectorvs Unvaccinated
1.31(0.72–2.36)
Observational data: associations, not effects.
Further findings
Myositis after each specific first, second and third mRNA dose · 180 days
- Estimates similar to the estimate of all doses combined
Parts of this Brief are withheld: the automatic checks could not confirm them against the abstract.
Original publication
SARS-CoV-2 vaccination and myositis in Norway and Sweden. Rheumatology (Oxford). Published 22 November 2025. doi:10.
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