Background Data on serological immunity after three doses and the long-term immunogenicity (persistence) of COVID-19 vaccine in patients with inflammatory rheumatic diseases (IRD) treated with different immunomodulating drugs are still limited.Objectives To elucidate if 1) a third dose COVID-19 vaccine improves antibody responses, compared to two doses, in patients with IRD treated with biologic or targeted synthetic DMARD (b/tsDMARDs) treatment given as monotherapy or in combination with conventional synthetic DMARDs (csDMARDs) compared to controls, and 2) the persistence of antibody response after two doses of COVID-19 vaccine in IRD patients.Methods Antibody levels to two antigens representing Spike full length protein and Spike S1 and a Nucleocapsid C-terminal fragment (used to confirm previous COVID-19 infection) were measured in serum samples collected 2-12 and 21-40 weeks after the second vaccine dose and 2-12 weeks after the third dose using a multiplex bead-based serology assay. A sufficient antibody response (seropositivity) was defined as having antibodies over the cut-off level for both spike antigens (1). WT (wild type) anti-Spike IgG and omicron BA.1 and BA.2 variants were measured. Patients with IRD receiving immunomodulating treatment, regularly followed at a rheumatology department and a group of controls were recruited from five Swedish region.Results In total, 323 of 414 patients with IRD and 36 controls who received three vaccine doses participated in this part of the study. Following treatment groups were included: rituximab (n=118; 68% female; mean age 67 years), abatacept (n=18; 72% female; mean age 64 years), IL6r inhibitors (n=60; 73% female; mean age 64 years), JAK-inhibitors (n=44; 80% female, mean age 52 years), TNF-inhibitors (n=59; 70% female; mean age 47 years;), IL12/23/17 inhibitors (n=24; 46% female; mean age 54 years) and controls (n=36; 75% female, mean age 51 years). b/ts DMARD treatment was given as monotherapy or in combination with csDMARD, methotrexate (MTX) being the most frequently used csDMARD (32.5%). Compared to results after two vaccine doses, proportion (%) of seropositivity after three vaccine doses increased significantly in groups rituximab +/- DMARD (p=0.003 and p=0.004, respectively), IL6r inhibitors +DMARD (p=0.02), and abatacept+DMARD (p=0.01). However, the proportion of seropositivity after three vaccine doses was still significantly lower in rituximab treated patients (52%) compared to other treatment groups or controls (p<0.001) (Figure 1A/B). Antibody response to WT, omicron sBA.1 and sBA.2 showed similar pattern with the lowest levels among patients treated with rituximab.

When antibody response was compared between 2-12 weeks and 21-40 weeks after second dose, the proportion of seropositive rituximab treated patients decreased from 34.9 % to 32.6%. All patients with JAK inhibitors and with JAK-inhibitors and IL6r-inhibitors seropositive 21-40 weeks after the second vaccine dose. Patients treated with other bDMARDs were not included in this analysis due to limited number participants.Conclusion In this Swedish study including IRD patients receiving different b/t DMARDs, a sufficient immunogenicity of the third dose of COVID-19 vaccine was observed in all treatments with exception for rituximab. However, the increased proportion of seropositivity after the third COVID-19 vaccine doses in rituximab and other patients with insufficient response to two doses including response to the omicron variants, supports the current recommendations on additional booster doses. The immunogenicity of two vaccine doses was preserved to 40 weeks in majority of patients treated with different immunomodulating treatment with exception for rituximab.