medwireNews: Researchers have developed a calculator that could help clinicians predict the probability of a seropositive immunogenic response to mRNA SARS-CoV-2 vaccination in patients with autoimmune inflammatory rheumatic diseases (AIIRDs) receiving rituximab.
The findings, presented at the ACR Convergence 2021 virtual meeting, expand on the results from a previously reported study showing the importance of an increased interval between rituximab treatment and vaccination to improve response to the BNT162b2 (Pfizer–BioNTech) vaccine in AIIRD patients.
The latest research involved 108 AIIRD patients taking rituximab, of whom 45.4% had rheumatoid arthritis, 21.3% antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis, 16.7% idiopathic inflammatory myopathy, 10.2% systemic lupus erythematosus, and 5.6% other types of systemic vasculitis.
These AIIRD patients had a significantly lower response rate to the BNT162b2 vaccine than 122 non-immunocompromised controls, as well as significantly reduced mean serum S1/S2 immunoglobulin (Ig)G titers, at 41.67% versus 100% and 51.01 BAU versus 218.39 BAU, respectively.
The 45 patients who responded to the vaccine had significantly higher average serum IgG levels than the 63 who did not, at 1189.78 versus 884.33 mg/dL, a lower cumulative rituximab dose (median 4000 vs 8000 mg), fewer rituximab treatment courses (median of three vs five), and a longer mean interval between rituximab treatment and vaccination (469.82 vs 162.08 days).
Presenting author Victoria Furer (Tel Aviv Sourasky Medical Center, Israel) reported logistic regression analysis showing that patients diagnosed with ANCA-associated vasculitis or idiopathic inflammatory myositis had a significantly reduced likelihood of a response relative to those with rheumatoid arthritis, at odds ratios (ORs) of 0.21 and 0.19, respectively.
By comparison, the likelihood of a response was significantly increased in those patients with high serum IgG levels prior to the last course of rituximab (OR=1.1 for every 50 mg/dL increment) and a longer interval between treatment and vaccination (OR=1.0).
Furer noted that these predictive factors were confirmed in an independent validation cohort of 48 AIIRD patients taking rituximab, of whom 21 responded to the vaccine and 27 did not, and when used in a calculator predicted the likelihood for immunogenicity in these patients with 59.3% specificity and 90.5% sensitivity. The positive predictive value was 63.4% and the negative predictive value was 89.9%.
“The use of the predicting calculator may optimize scheduling of rituximab treatment and COVID-19 vaccination in these challenging patients,” said Furer.
However, she added that the applicability of the findings to other SARS-CoV-2 vaccines is not yet clear, and there were no data available on CD19 cell counts and vaccine-induced T-cell immunity.
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