Incidence, features, and outcome of disease relapse after COVID-19 vaccination in patients with idiopathic inflammatory myopathies.

INTRODUCTION/AIMS: Vaccination against coronavirus disease 2019 (COVID-19) is relatively safe in patients with idiopathic inflammatory myopathies (IIM); however, myositis flares following vaccination have been poorly studied. We aimed to evaluate the frequency, features, and outcomes of disease relapses in patients with IIM following COVID-19 vaccination. METHODS: A cohort of 176 IIM patients were interviewed after the third wave of the COVID-19 pandemic and followed prospectively. Relapses were determined using the disease state criteria and the outcome of the flares with myositis response criteria, calculating the total improvement score (TIS). RESULTS: A total of 146 (82.9%) patients received a vaccination, 17/146 (11.6%) patients had a relapse within 3 mo, and 13/146 (8.9%) patients within 1 mo. The relapse rate of unvaccinated patients was 3.3%. Three months after the post-vaccination relapses, 70.6% of the patients (12/17) achieved an improvement of disease activity (average TIS score: 30 ± 15.81; seven minor, five moderate, and zero major improvements). Six months after flares improvement was detected in 15/17(88.2%) of relapsed patients (average TIS score: 43.1 ± 19.53; 3 minimal, 8 moderate, and 4 major). Forward stepwise logistic regression analysis revealed that the active state of myositis at the time of injection (p < .0001; odds ratio, 33; confidence interval, 9-120) was significantly associated with the occurrence of a relapse. DISCUSSION: A minority of the vaccinated IIM patients had a confirmed disease flare after COVID-19 vaccination and the majority of the relapses improved after individualized treatment. An active disease state at the time of vaccination probably contributes to the increased risk of a post vaccination myositis flare.