To Örebro University

Background/Aims: Flares following COVID-19 vaccination are an emerging concern among patients with rare rheumatic disease like idiopathic inflammatory myositis (IIMs), whereas data and understanding of this is rather limited. We aimed to study the prevalence, characteristics and determinants of IIM flares following COVID-19 vaccination.

Methods: CoVAD (COVID-19 Vaccination In Autoimmune Diseases) surveys are global patient self-reported e-surveys from 109 countries conducted in 2021 and 2022. Flares of IIM were defined by 4 definitions; a. patient self-reported, b. physician and immunosuppression (IS) denoted, c. sign directed (new erythematous rash, or worsening myositis or arthritis), d. MCID worsening of PROMISPF10a score between the patients who had taken both surveys. Descriptive statistics and multivariate regression were used to describe the predictors of flare. Cox-regression analysis was used to differentiate flares by IIM subtypes.

Results: Among the 1,278 IIM patients, aged 63 (50-71) years, 276 (21.5%) were dermatomyositis, 237 (18.5%) IBM, 899 (70.3%) were female and most were Caucasian (80.8%). Flares of IIM were seen in 123/1278 (9.6%), 163/1278 (12.7%), 112/1278 (8.7%), and 16/96 (19.6%) by definitions a-d respectively with median time to flare being 71.5 (10.7-235) days. Muscle weakness (69.1%), and fatigue (56.9%) were the most common symptoms of flare. The predictors of self-reported flare were: inactive/disease in remission prior to first dose of vaccine (OR ¼ 4.3, 95%CI¼2.4-7.6), and anxiety disorder (OR ¼ 2.2, 95%CI¼1.1-4.7). Rituximab use (OR ¼ 0.3, 95%CI¼0.1-0.7) and IBM (OR ¼ 0.3, 95%CI¼0.1-0.7) were protective. Physician defined flares were seen more often in females, mixed ethnicity, and those with asthma, ILD, and anxiety disorder (OR ranging 1.6-7.0, all p < 0.05). Notably, overlap myositis (OM) had higher HR for flare compared to polymyositis (HR ¼ 2.3, 95%CI¼1.2-4.4, p ¼ 0.010).

Conclusion: Nearly one in ten individuals with IIM develop flares after vaccination, more so among women, those with overlap myositis, and inactive disease prior to vaccination. Formal definition of flares in IIM is needed.