Antibody response to a single dose of SARS-CoV-2 mRNA vaccine in patients with rheumatic and musculoskeletal diseases The immune response to SARS-CoV-2 messenger RNA (mRNA) vaccines in patients with rheumatic and musculoskeletal diseases (RMD) is undefined because these individuals were largely excluded from phase I-III studies. To better understand the immune response to vaccination in this patient population, we studied the antibody response in patients with RMD who completed the first dose of SARS-CoV-2 mRNA vaccination. Participants with RMD across the USA were recruited to participate in this prospective cohort via social media. Those with prior SARS-CoV-2 were excluded. We collected demographics, RMD diagnoses and immunomodulatory regimens and tested for SARS-CoV-2 antibodies at baseline and prior to the second vaccine dose. Antibody testing was conducted on the semiquantitative Roche Elecsys anti-SARS-CoV-2 S enzyme immunoassay (EIA) which tests for antibodies against the receptor-binding domain (RBD) of the SARS-CoV-2 spike protein. 1 We evaluated the association between demographic/clinical characteristics and positive antibody response using Fisher's exact test and Wilcoxon rank-sum test. We studied 123 participants who received their first SARS-CoV-2 vaccination dose between

Figure 1 Anti-SARS-CoV-2 RBD antibody titre overall (n=403*) and by medications associated with a negative antibody response: mycophenolate included in regimen (n=41), rituximab included in regimen (n=19), glucocorticoid included in regimen (n=116) and glucocorticoid monotherapy (n=8) in patients with RMD after twodose SARS-CoV-2 mRNA vaccination. Results range from <0.4 to >250 U/mL with positive antibody defined as an anti-SARS-CoV-2 RBD antibody titre >0.79 U/mL by the manufacturer; blue data points indicate median titre. *One titre value was missing from the total N (404). RBD, receptor binding domain; RMD, rheumatic and musculoskeletal disease.

To evaluate disease flare and postvaccination reactions (reactogenicity) in patients with rheumatic and musculoskeletal diseases (RMDs) following 2-dose SARS-CoV-2 messenger RNA (mRNA) vaccination.Methods. RMD patients (n = 1,377) who received 2-dose SARS-CoV-2 mRNA vaccination between December 16, 2020 and April 15, 2021 completed questionnaires detailing local and systemic reactions experienced within 7 days of each vaccine dose (dose 1 and dose 2), and 1 month after dose 2, detailing any flares of RMD. Associations between demographic/clinical characteristics and flares requiring treatment were evaluated using modified Poisson regression.Results. Among the patients, 11% reported flares requiring treatment; there were no reports of severe flares. Flares were associated with prior SARS-CoV-2 infection (incidence rate ratio [IRR] 2.09, P = 0.02), flares in the 6 months preceding vaccination (IRR 2.36, P < 0.001), and the use of combination immunomodulatory therapy (IRR 1.95, P < 0.001). The most frequently reported local and systemic reactions included injection site pain (87% after dose 1, 86% after dose 2) and fatigue (60% after dose 1, 80% after dose 2). Reactogenicity increased after dose 2, particularly for systemic reactions. No allergic reactions or SARS-CoV-2 diagnoses were reported.Conclusion. Flares of underlying RMD following SARS-CoV-2 vaccination were uncommon. There were no reports of severe flares. Local and systemic reactions typically did not interfere with daily activity. These early safety data can help address vaccine hesitancy in RMD patients.The analyses described here are the responsibility of the authors alone and do not necessarily reflect the views or policies of the Department of Health and Human Services, nor does mention of trade names, commercial products, or organizations imply endorsement by the US Government.

Supplemental Digital Content is available in the text.